For U# 1.2b1 see the releases page

If you want to report issues for VRChat to look at fixing in the main SDK, report them at https://github.com/vrchat-community/UdonSharp.

Otherwise be aware that this now houses a new release with some additional U# features which is somewhat jank and I don't advise you use it if you're looking at distributing prefabs. Go to the release link here if you are still interested https://github.com/MerlinVR/UdonSharp/releases/tag/v1.2.0-b1