This is due to the two breaking changes in Forge.
Version: 1.21.1

@MelanX Your issue is fixed with #38. We have to wait until @r8420 will merge it.

You can use my current release for 1.19 which is exactly the same as in the PR.
https://github.com/drjayy/MoreOverlays-updated/releases/tag/v1.21.2

-> Please leave this issue open so it is used as reference for the PR (aka r8420 will see it)

@MelanX this issue can be closed as the PR is now officially merged

Should be fixed in MoreOverlays 1.21.2