I cover those and have done some very awkard spots and on the ceiling! But since you are tearing all out and painting and spackling I'd do another something like this - but also bring it up higher (when the light is removed you will see the fixture and how you can cut into the wall and go up higher if needed) https://www.wayfair.com/lighting/pdp/orren-ellis-shequita-6-light-black-flush-mounted-sconce-w007684027.html This is only 3' in one direction so the photos are misleading, but a flush mount LED ceiling light may work there. Or this - https://www.wayfair.com/lighting/pdp/orren-ellis-shoji-1-light-dimmable-led-vanity-light-w007437834.html

Some ideas…

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I would consider mirroring the entire wall and having the light fixture(s) mounted through the mirror. To hell with "dated" or whatever objection , that's a solution that works better than trying to fit a round or square peg into a triangular hole.

I like Pal’s suggestion, but if you don’t then how about having mirror made that goes straight across?