With a gui I guess, right? Not one that is run by terminal commands. Did you search or try any emulator yet and is something too big or does not work for you? What environment are you in and what repository do you can use? Even if the filesize of the emulator is small, it might introduce lot of dependencies that are much bigger in size. How old is the PC actually? Ancient? How smol do you need it?
You could also just download an .AppImage file, which does not require you to install anything and all dependencies are included in this one file. So while the file looks big (15 MB for recent build Snes9x 1.62.3), it still is all you need, compared to an installation from your package manager: https://github.com/snes9xgit/snes9x/releases