>>296736783
Yeah, this is made for Blender animation and not MMD, so sometimes CATS tool can't deal with it. You might have to manually merge and reparent the armatures, remove the custom shapes, clear the animation data, merge bones down to just the ones that VRChat would use, and then manually adjust the weight painting.

My suggestion is to come back to it in a few months when you've got a more solid grasp on the program, and to find an MMD model to work with for now.