I have tried adding all the recent optifine versions (G6 G7 and pre11) and all are giving me seemingly the exact same problem, optifabric 1.9.6 is loading properly on its own, I get the error after adding optifine (I have tried both adding original jar into mod folder as well as extracting into plain 1.16.5 fabric instance then adding it to the problem instance). Other than that here's the log, I hope someone can help because I'm not very good at troubleshooting but I tried! https://paste.ee/p/OjIve

Edit: in case it is useful I am attempting to add optifine to the All of Fabric 3 modpack

I have the same issue, but it crashes at

Caused by: org.spongepowered.asm.mixin.injection.throwables.InjectionError: Critical injection failure: Redirector cullParticles(Lnet/minecraft/class_703;Lnet/minecraft/class_4588;Lnet/minecraft/class_4184;F)V in cullparticles.mixins.json:MixinParticleManager failed injection check, (0/1) succeeded. Scanned 1 target(s). Using refmap cullparticles-refmap.json