Can't Paint in Texture Painter

I’ve looked for what has worked for other people but none of the fixes are working. Can someone look at the attached file and help me figure out why I can’t paint in texture paint? https://drive.google.com/file/d/10qybvIDgkR-VLeLwaWkIyVdXHQZHrfAR/view?usp=sharing!Dragon (2)|690x436

You might get more takers with a smaller file. Make a copy and delete excess geometry, and also select compress when saving if you don’t already, until you get the size down to about <5mb. The smallest file, that still demonstrates the issue, is ideal.

Alternatively (or, additionally) tell us how exactly the issue manifests and what steps you’ve taken so far in attempting to fix it.