If your main issue is with downloads and file sizes, what makes you think that switching to PC will remedy that? If you sell your Xbox and exclusively use your PC, you'll face the same issue just on a different platform.

My opinion - keep the Series X and use it, your PC, and your Switch. It doesn't sound like there's much of a benefit in selling it.

Actually, assuming you have access to MS Game Pass, there are lots of fantastic experiences that are under 10gb. To name a few: Tunic, Dead Cells, Hollow Knight, Crusader Kings, the Ori series, Prodeus, and Slay The Spire. If you have access to Game Pass, I'd suggest giving any of those a whirl.