Yuzu is better overall, but Ryujinx works weirdly better for certain games. Like, Mario Wonder runs about 40% better for me on Ryujinx for some reason.

The steam deck library includes the entire switch library via emulation, so Yeah Obviously. (Ik they’re not counting emulation, but my point is that the steam deck is a PC, which makes it much more versatile)

Try setting it to use proton experimental, newer games sometimes depend on features that aren’t in the stable versions of proton yet (or are at least buggier/worse in the stable versions)

Edit: also try launching the game from desktop mode. The compositor in steam mode is Wayland-based and desktop mode uses an X11 session by default. The issues you’re describing sound a bit like something that’s happened to me running games under Wayland on my laptop