java.io.UncheckedIOException: Error transforming /Applications/MultiMC.app/Contents/MacOS/instances/Fabric 1.16.5/.minecraft/.optifine/OptiFine_1.16.5_HD_U_G8/Optifine-mod.jar
at me.modmuss50.optifabric.util.ZipUtils.transform(ZipUtils.java:98)
at me.modmuss50.optifabric.mod.OptifineSetup.getRuntime(OptifineSetup.java:115)
at me.modmuss50.optifabric.mod.OptifabricSetup.run(OptifabricSetup.java:41)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1510)
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:667)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.prepareConfigs(MixinProcessor.java:542)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.select(MixinProcessor.java:439)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.checkSelect(MixinProcessor.java:415)
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:285)
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:208)
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:178)
at org.spongepowered.asm.mixin.transformer.FabricMixinTransformerProxy.transformClassBytes(FabricMixinTransformerProxy.java:23)
at net.fabricmc.loader.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:157)
at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:150)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:427)
at net.fabricmc.loader.util.DefaultLanguageAdapter.create(DefaultLanguageAdapter.java:45)
at net.fabricmc.loader.EntrypointStorage$NewEntry.create(EntrypointStorage.java:112)
at net.fabricmc.loader.EntrypointStorage$NewEntry.getOrCreate(EntrypointStorage.java:99)
at net.fabricmc.loader.EntrypointStorage.lambda$getEntrypointContainers$1(EntrypointStorage.java:184)
at net.fabricmc.loader.entrypoint.EntrypointContainerImpl.getEntrypoint(EntrypointContainerImpl.java:37)
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:50)
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke(EntrypointUtils.java:36)
at net.fabricmc.loader.launch.knot.Knot.init(Knot.java:137)
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:28)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:196)
at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:231)
at org.multimc.EntryPoint.listen(EntryPoint.java:143)
at org.multimc.EntryPoint.main(EntryPoint.java:34)
Caused by: java.util.zip.ZipException: zip END header not found
at java.base/java.util.zip.ZipFile$Source.zerror(ZipFile.java:1482)
at java.base/java.util.zip.ZipFile$Source.findEND(ZipFile.java:1383)
at java.base/java.util.zip.ZipFile$Source.initCEN(ZipFile.java:1390)
at java.base/java.util.zip.ZipFile$Source.(ZipFile.java:1221)
at java.base/java.util.zip.ZipFile$Source.get(ZipFile.java:1184)
at java.base/java.util.zip.ZipFile$CleanableResource.(ZipFile.java:718)
at java.base/java.util.zip.ZipFile.(ZipFile.java:238)
at java.base/java.util.zip.ZipFile.(ZipFile.java:168)
at me.modmuss50.optifabric.util.ZipUtils.transform(ZipUtils.java:103)
at me.modmuss50.optifabric.util.ZipUtils.transform(ZipUtils.java:95)
... 35 more

Issue solved, just jad to dowwnload another 1.16.5 version of optifine