I'm so confused... Whenever I try to add this polygon group, it gives me this error, and I'm not sure how to fix it? All the names are fully unique, so that's not the problem. If you have any information what could be broken, that would be a lifesaver
Update, if I try to use Sprite2d, it's a COMPLETELY DIFFERENT error???
That's alright. Itch's notifications can be weird occasionally.
But anyway, an important part ot Godot's 2D skeletal rigging is that Sprite2Ds and Polygon2Ds are set up in fundamentally different ways. Polygon2Ds involve weight painting each vertex to one or more bones. There's a good forum post you can read about the topic.
As for Sprite2Ds, they're set up in a much more simple manner. They do not belong to a "polygon group", and instead, you simply need to make a Sprite2D the child of a Bone2D, and it should work out fine. A Sprite2D-based skeletal setup does not need to involve any polygon groups, as you will just need you to select the relevant Skeleton2D instead.