Yes, the only 3.x feature we support, is their renaming of skinnedmesh, to weightedmesh to mesh, so that you can at least open older animations.
As for what we don't support, no we don't have a clear list. I know two of two new things that are unsupported: shear matrices, and linked meshes. But, other than that, simply all new features from 3.0 and forward, we don't support.
Recently, one of our artists happened to get affected by this, since they exported the file from a newer spine editor. The advice then was to reexport it in an older version 2.x, and compare the files to see what feature is actually afffected.
"I have no problem with it renaming of all "mesh" to "weightedmesh" solved my problem."
The editor does this automatically for you now. Is it still a problem for you?