First error is a stated in the picture where it is only a problem with the "customavatar.unity3d" that Unity is outputting is not found since it is looking for "customAvatar.unity3d"

This is not a large problem to fix but it isn't in the cs files and probably is in the dll's so it needs to be changed on the developers end.

Second, if I make a link to the file so the SDK finds the correct file that way and the upload UI is shown in the Game tab in unity.

When i then his upload, this second error occurred in the second and third image.

I know Linux is not supported, but it looks to almost be at the point that it does and (for me) VRChat runs pretty well (not perfect) with Steam Proton.

Please contact me for any and all questions or additional information.