First off happy that Optifabric has been updated. Thanks Choco!

So when Fabric API is in the folder along with Optifabric/Optifine - the game will load just fine, but crashes upon log in to a world.

I am using:
Optifine 1.20.1_HD_U_I5
fabric-api-0.85.0+1.20.1

Here is the crash log:

https://pastebin.com/LQeC2kVf

Could you provide more context? I was not able to replicate this issue, but from the logs it looks like it has something to do with Fabric Networking API