As far as a standalone version of PPSSPP (PSP emulation) goes, the Switch port of SDL2, as far as I know, hasn't yet been updated to support OpenGL as of this writing (however, it's a work in progress on the Github repo, which you can watch
here ), that's one major hurdle. There's also an issue of needing implementations of something called "std::mutex" and "std::thread", but this shouldn't be too hard to do. Getting PPSSPP's ARM64 JIT to work should also not be that difficult.
As for the libretro version, I'm not sure where that stands.