Take a break, do something else.
I'm not an artist but a software developer and electronics engineer and I often had similar problems in that I couldn't make decisions about which approach to use to solve a problem and couldn't motivate myself to think up better ways of solving problems. I would be in a state where I'd be just staring at a sheet of paper or a screen getting nothing done.
Sometimes it was enough to to just get away from my desk and go for a walk in the sunshine and think about something else, or indeed nothing at all. Coming back to my desk after half an hour in the fresh air I would sometimes have the solution spring almost fully formed from my fingers to the paper or keyboard even though I hadn't been consciously thinking about the problem.
It has sometimes been necessary to just drop the problem entirely for days, on occasion for weeks.
Something that might also help is this: I found it easier to push myself into creating novel solutions when I was working than I do now that I am retired. Deadlines and the feeling that others are depending on me finding inspiration helped prevent me demanding perfection rather than performance. Now that I have only myself to satisfy it is easy to feel that none of it is worth working on and I get much less done.
So perhaps you should try creating a deadline or some other need to get something done. You could offer to create something for someone else.
Does any of that sound useful?
