People always accidentally hit the screenshot and home buttons on my Joy-Cons, especially using single Joy-Cons for party games and such. These are two simple rings that can be stuck to your Joy-Cons with any adhesive of choice (I used clear scotch double-sided tape) that's thin enough.

Should print with little to no fuss. Use a brim if you have adhesion issues. Wouldn't recommend a raft, since a smooth surface on the bottom will help with adhesion.

I make guards like this for any buttons in my life that I accidentally press a lot, like my dishwasher!