Nintendo Switch Online's "Labs" section offers a selection of indie games and experiences, often with a focus on classic game styles. These games are developed by third-party studios and may offer unique twists on classic gameplay.
If you own a moddable Switch (early units) and legally dump your own Genesis ROMs from cartridges you own, you can use: SEGA-GENESIS-NINTENDO-SWITCH-ONLINE-NSP-ROMSLAB...
: Official NSO apps verify membership every seven days. Custom NSPs often bypass this check to allow permanent offline play. Nintendo Switch Online's "Labs" section offers a selection