We need to use humanoid avatars for root motion, but we cannot get transform masks to work on these avatars? Does it simply not work?
There is so little documentation on this that it is really not clear what we should expect. The notion that Unity simply does not allow you to use extra bones on a humanoid rig is crazy.
I believe you’re supposed to use humanoid masks on humanoid models.
That being said, I vaugely remember transform masks working on humanoid models last time we used Humanoid, but that game shipped on Unity 2018, so I might be missremembering. But I think that if your bone hierarchy matches the mask hierarchy, it should work. You’d of course have to make a unique mask for every mesh that has a unique rig, whereas if you use a humanoid mask you’d be able to share it.