Ok, I’ve not done fine art in a long time so I’ll try and adapt what helps me when I feel like you do in case it helps you:

Try something slightly different that you don’t care about but is in the same technique space, e.g. go paint a Warhammer 40k miniature and just play with how good you can get it. It’ll use the same skill but you won’t care or feel pressure for it to be perfect, it’s disposable after all, and then you’ll feel better and do better on your next piece/canvas that you actually care about.