looking at the recent announcement of the closure of the wiiu and 3ds eshops, people can still play their downloaded games even once the service is down, with the nso once the service stops or a game is delisted then it is unable to be played.
My policy for these will be that I'll only be doing games that aren't available on digital storefronts like Steam and GOG - those options are already there for you if you want to play those games - these are for games where no such option is available and your only choice is to buy it off a guy on ebay (assuming you have a disc drive) or download an iso (either of which also assumes you know your way around DOSBox, in the case of DOS games).
Debian/Ubuntu based distributions like Pop!_OS can install applications from .deb files. These files function like .dmg files on macOS; opening a downloaded .deb file launches the installer program "Eddy" and puts the installed application in the correct folder.
You can download up-to-date binaries for all platforms supported upstream (Debian and some RPM based distributions with the classic AppImageLauncher, almost any somewhat recent distribution with AppImageLauncher Lite) from the GitHub release page. 2b1af7f3a8