If I download Fabric API and OptiFabric at the same time while on game version 1.20.4, I get stuck on the Mojang loading screen. Could you please advise on how to resolve this?

Depends on the version of Fabric Loader, Fabric API, Optifabric, and Optifine versions you are using.

Could you share the latest.log file from your logs folder?
I was able to get to the main menu of Minecraft using Minecraft 1.20.4, Fabric Loader 0.15.11, Fabric API 0.97.0, OptiFabric 1.14.3, and OptiFine HD U I7.

java.lang.RuntimeException: Error running OptiFine patcher at D:\mc整合.minecraft\versions\1.20.4-Fabric 0.15.11-OptiFine_I7\mods\OptiFine_1.20.4_HD_U_I7.jar on D:\mc整合.minecraft\versions\1.20.4-Fabric 0.15.11-OptiFine_I7\1.20.4-Fabric 0.15.11-OptiFine_I7.jar
at me.modmuss50.optifabric.mod.OptifineSetup.runInstaller(OptifineSetup.java:231)
at me.modmuss50.optifabric.mod.OptifineSetup.getRuntime(OptifineSetup.java:109)
at me.modmuss50.optifabric.mod.OptifabricSetup.run(OptifabricSetup.java:46)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
at com.chocohead.mm.Plugin.getMixins(Plugin.java:340)
at org.spongepowered.asm.mixin.transformer.PluginHandle.getMixins(PluginHandle.java:128)
at org.spongepowered.asm.mixin.transformer.MixinConfig.postInitialise(MixinConfig.java:796)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.prepareConfigs(MixinProcessor.java:568)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.select(MixinProcessor.java:462)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.checkSelect(MixinProcessor.java:438)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:290)
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:234)
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:202)
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:422)
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.tryLoadClass(KnotClassDelegate.java:323)
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.loadClass(KnotClassDelegate.java:218)
at net.fabricmc.loader.impl.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:119)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:467)
at net.fabricmc.loader.impl.util.DefaultLanguageAdapter.create(DefaultLanguageAdapter.java:50)
at net.fabricmc.loader.impl.entrypoint.EntrypointStorage$NewEntry.getOrCreate(EntrypointStorage.java:117)
at net.fabricmc.loader.impl.entrypoint.EntrypointContainerImpl.getEntrypoint(EntrypointContainerImpl.java:53)
at net.fabricmc.loader.impl.FabricLoaderImpl.invokeEntrypoints(FabricLoaderImpl.java:384)
at net.fabricmc.loader.impl.launch.knot.Knot.init(Knot.java:160)
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:68)
at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at oolloo.jlw.Wrapper.invokeMain(Wrapper.java:71)
at oolloo.jlw.Wrapper.main(Wrapper.java:51)
Caused by: java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at me.modmuss50.optifabric.mod.OptifineSetup.runInstaller(OptifineSetup.java:229)
... 32 more
Caused by: java.util.zip.ZipException: invalid distance too far back
at java.base/java.util.zip.InflaterInputStream.read(InflaterInputStream.java:164)
at java.base/java.io.FilterInputStream.read(FilterInputStream.java:106)
at optifine.Utils.readAll(Utils.java:147)
at optifine.Patcher.process(Patcher.java:81)
... 37 more

[10:13:46] [main/INFO]: Loading Minecraft 1.20.4 with Fabric Loader 0.15.11
[10:13:46] [main/INFO]: Fabric is preparing JARs on first launch, this may take a few seconds...
[10:13:46] [main/ERROR]: Incompatible mods found!
net.fabricmc.loader.impl.FormattedException: net.fabricmc.loader.impl.discovery.ModResolutionException: Mod discovery failed!
at net.fabricmc.loader.impl.FormattedException.ofLocalized(FormattedException.java:63) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.FabricLoaderImpl.load(FabricLoaderImpl.java:197) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.launch.knot.Knot.init(Knot.java:146) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:68) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23) ~[fabric-loader-0.15.11.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:568) ~[?:?]
at oolloo.jlw.Wrapper.invokeMain(Wrapper.java:71) ~[?:?]
at oolloo.jlw.Wrapper.main(Wrapper.java:51) ~[?:?]
Caused by: net.fabricmc.loader.impl.discovery.ModResolutionException: Mod discovery failed!
at net.fabricmc.loader.impl.discovery.ModDiscoverer.lambda$discoverMods$1(ModDiscoverer.java:159) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.util.ExceptionUtil.gatherExceptions(ExceptionUtil.java:33) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.discovery.ModDiscoverer.discoverMods(ModDiscoverer.java:159) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.FabricLoaderImpl.setup(FabricLoaderImpl.java:215) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.FabricLoaderImpl.load(FabricLoaderImpl.java:192) ~[fabric-loader-0.15.11.jar:?]
... 9 more
Caused by: java.lang.RuntimeException: java.lang.RuntimeException: Error analyzing [D:\mc .minecraft\versions\1.20.4-Fabric 0.15.11-OptiFine_I7\mods\OptiFine_1.20.4_HD_U_I7.jar]: java.util.zip.ZipException: invalid CEN header (bad signature)
at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77) ~[?:?]
at jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[?:?]
at java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499) ~[?:?]
at java.lang.reflect.Constructor.newInstance(Constructor.java:480) ~[?:?]
at java.util.concurrent.ForkJoinTask.getThrowableException(ForkJoinTask.java:562) ~[?:?]
at java.util.concurrent.ForkJoinTask.reportExecutionException(ForkJoinTask.java:604) ~[?:?]
at java.util.concurrent.ForkJoinTask.get(ForkJoinTask.java:981) ~[?:?]
at net.fabricmc.loader.impl.discovery.ModDiscoverer.discoverMods(ModDiscoverer.java:156) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.FabricLoaderImpl.setup(FabricLoaderImpl.java:215) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.FabricLoaderImpl.load(FabricLoaderImpl.java:192) ~[fabric-loader-0.15.11.jar:?]
... 9 more
Caused by: java.lang.RuntimeException: Error analyzing [D:\mc .minecraft\versions\1.20.4-Fabric 0.15.11-OptiFine_I7\mods\OptiFine_1.20.4_HD_U_I7.jar]: java.util.zip.ZipException: invalid CEN header (bad signature)
at net.fabricmc.loader.impl.discovery.ModDiscoverer$ModScanTask.compute(ModDiscoverer.java:300) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.discovery.ModDiscoverer$ModScanTask.compute(ModDiscoverer.java:249) ~[fabric-loader-0.15.11.jar:?]
at java.util.concurrent.RecursiveTask.exec(RecursiveTask.java:100) ~[?:?]
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373) ~[?:?]
at java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182) ~[?:?]
at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655) ~[?:?]
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622) ~[?:?]
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165) ~[?:?]
Caused by: java.util.zip.ZipException: invalid CEN header (bad signature)
at java.util.zip.ZipFile$Source.zerror(ZipFile.java:1730) ~[?:?]
at java.util.zip.ZipFile$Source.checkAndAddEntry(ZipFile.java:1191) ~[?:?]
at java.util.zip.ZipFile$Source.initCEN(ZipFile.java:1669) ~[?:?]
at java.util.zip.ZipFile$Source.(ZipFile.java:1447) ~[?:?]
at java.util.zip.ZipFile$Source.get(ZipFile.java:1409) ~[?:?]
at java.util.zip.ZipFile$CleanableResource.(ZipFile.java:717) ~[?:?]
at java.util.zip.ZipFile.(ZipFile.java:251) ~[?:?]
at java.util.zip.ZipFile.(ZipFile.java:180) ~[?:?]
at java.util.zip.ZipFile.(ZipFile.java:194) ~[?:?]
at net.fabricmc.loader.impl.discovery.ModDiscoverer$ModScanTask.computeJarFile(ModDiscoverer.java:321) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.discovery.ModDiscoverer$ModScanTask.compute(ModDiscoverer.java:290) ~[fabric-loader-0.15.11.jar:?]
at net.fabricmc.loader.impl.discovery.ModDiscoverer$ModScanTask.compute(ModDiscoverer.java:249) ~[fabric-loader-0.15.11.jar:?]
at java.util.concurrent.RecursiveTask.exec(RecursiveTask.java:100) ~[?:?]
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373) ~[?:?]
at java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182) ~[?:?]
at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655) ~[?:?]
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622) ~[?:?]
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165) ~[?:?]

Mine is the same as the mods version you mentioned, and I can't get in either.

java.lang.RuntimeException: Error running OptiFine patcher at D:\mc整合.minecraft\versions\1.20.4-Fabric 0.15.11-OptiFine_I7\mods\OptiFine_1.20.4_HD_U_I7.jar on D:\mc整合.minecraft\versions\1.20.4-Fabric 0.15.11-OptiFine_I7\1.20.4-Fabric 0.15.11-OptiFine_I7.jar at me.modmuss50.optifabric.mod.OptifineSetup.runInstaller(OptifineSetup.java:231) at me.modmuss50.optifabric.mod.OptifineSetup.getRuntime(OptifineSetup.java:109) at me.modmuss50.optifabric.mod.OptifabricSetup.run(OptifabricSetup.java:46) at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) at com.chocohead.mm.Plugin.getMixins(Plugin.java:340) at org.spongepowered.asm.mixin.transformer.PluginHandle.getMixins(PluginHandle.java:128) at org.spongepowered.asm.mixin.transformer.MixinConfig.postInitialise(MixinConfig.java:796) at org.spongepowered.asm.mixin.transformer.MixinProcessor.prepareConfigs(MixinProcessor.java:568) at org.spongepowered.asm.mixin.transformer.MixinProcessor.select(MixinProcessor.java:462) at org.spongepowered.asm.mixin.transformer.MixinProcessor.checkSelect(MixinProcessor.java:438) at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:290) at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:234) at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:202) at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:422) at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.tryLoadClass(KnotClassDelegate.java:323) at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.loadClass(KnotClassDelegate.java:218) at net.fabricmc.loader.impl.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:119) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520) at java.base/java.lang.Class.forName0(Native Method) at java.base/java.lang.Class.forName(Class.java:467) at net.fabricmc.loader.impl.util.DefaultLanguageAdapter.create(DefaultLanguageAdapter.java:50) at net.fabricmc.loader.impl.entrypoint.EntrypointStorage$NewEntry.getOrCreate(EntrypointStorage.java:117) at net.fabricmc.loader.impl.entrypoint.EntrypointContainerImpl.getEntrypoint(EntrypointContainerImpl.java:53) at net.fabricmc.loader.impl.FabricLoaderImpl.invokeEntrypoints(FabricLoaderImpl.java:384) at net.fabricmc.loader.impl.launch.knot.Knot.init(Knot.java:160) at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:68) at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:568) at oolloo.jlw.Wrapper.invokeMain(Wrapper.java:71) at oolloo.jlw.Wrapper.main(Wrapper.java:51) Caused by: java.lang.reflect.InvocationTargetException at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:568) at me.modmuss50.optifabric.mod.OptifineSetup.runInstaller(OptifineSetup.java:229) ... 32 more Caused by: java.util.zip.ZipException: invalid distance too far back at java.base/java.util.zip.InflaterInputStream.read(InflaterInputStream.java:164) at java.base/java.io.FilterInputStream.read(FilterInputStream.java:106) at optifine.Utils.readAll(Utils.java:147) at optifine.Patcher.process(Patcher.java:81) ... 37 more

STOP HIJACKING OTHER'S TICKETS! Create your own ticket so that you can get help for your issue.

@pipixixi233 looks like your OptiFine jar file is corrupt. Download it again.

Is that right? It's just as weird that I tried to redownload it several times.

I went to the official website to download OptiFine again. How can you tell? I am also a java developer o. O, but thank you very much.

You didn't state whether downloading it again actually worked or not.

I said that because I read this line:

Caused by: java.lang.RuntimeException: Error analyzing [D:\mc .minecraft\versions\1.20.4-Fabric 0.15.11-OptiFine_I7\mods\OptiFine_1.20.4_HD_U_I7.jar]: java.util.zip.ZipException: invalid CEN header (bad signature)

java.util.zip.ZipException: invalid CEN header (bad signature)

usually means that its corrupt