Are you trying to set up a like Sonic 3 A.I.R.?
So, how can you play Sonic 3 & Knuckles on Steam using a ROM? The first thing you'll need is a Steam account and a copy of the game. Unfortunately, Sonic 3 & Knuckles is not available on Steam, but you can use a ROM to play the game. sonic 3 & knuckles steam rom
~/.local/share/Steam/SteamApps/common/Sega Classics/uncompressed ROMs/ Are you trying to set up a like Sonic 3 A
This is the ultimate way to play in 2025. It is not a "ROM" in the traditional sense, but it requires one to operate. Unfortunately, Sonic 3 & Knuckles is not available
You apply the Sonic 3 Complete patch directly to your legally extracted Steam ROM using an online or offline IPS patching tool.
. While officially delisted from sale on May 20, 2022, ahead of the release of Sonic Origins
Because the original Steam ROM is delisted, the only "official" way to get a ROM is to dump it from an original Genesis cartridge using hardware like a Retrode.