i was using Fabric 1.16.5 with baritone, simple voice chat, and optifabric (obviously) and this popped up.
ive never got this error before, so if i did something wrong while reporting this error, please tell me
here's what was said on the screen:
"(red) There was an error loading OptiFabric!
Failed to load OptiFine, please report this!
net/fabricmc/tinyremapper/IMappingProvider"
with two buttons at the bottom: "Open issues" and "Copy stack-trace"
once i clicked on "Copy stack-trace", here's what was on my clipboard:

java.lang.NoClassDefFoundError: net/fabricmc/tinyremapper/IMappingProvider 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:519) at java.base/java.lang.Class.forName0(Native Method) at java.base/java.lang.Class.forName(Class.java:466) 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) Caused by: java.lang.ClassNotFoundException: net.fabricmc.tinyremapper.IMappingProvider at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:636) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:519) at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.loadClass(KnotClassDelegate.java:226) at net.fabricmc.loader.impl.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:119) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:519) ... 25 more

Fabric Loader 0.15.0+ incompatibility was reported in #1261