@gaetan I'm using a PC monitor for now that has no aspect ratio settings. Even if it did though, that sounds like an annoying workaround, having to adjust it for N64 games and then turn it back for everything else.

I'm trying to play N64 games on my XU4 in Recalbox, and it seems to work pretty well, except for one thing: the games are stretched to 16:9. How can I disable this so I can play N64 games in their original 4:3 aspect ratio?