I think I know how to fix it. in the file that Anubiyo posted, change all the 37's to 47, the version range to 1.20.1 for identity dependencies, and the architectury dependencies to the latest 1.20.1 version of architectury. In forge/src/main/resources/pack.mcmeta, change the pack format to 15. Then you recompile it and it should work I think? I might be wrong (probably am).

Edit: In forge/src/main/resources/identity-forge.mixins.json and common/src/main/resources/identity.mixins.json change JAVA_16 to JAVA_17
Edit Edit: I'm just gonna link this into a new issue with the solution, and post any updates there.

Originally posted by @NugglinGaming in #668

I'll be posting any extra findings here, and feel free to help me out here.

Posting this also in pull requests

Unfortunately your fix didn't work for me, I get the same result. I made the changes in your pull request and recompiled, but still crashes with only Identity and Architectury.

I hope this mod hasn't been abandoned, but it's starting to look like that is the case :(