Over the past few years I've been trying as much as possible to get away from buying games through DRM restricted sources, mainly buying from GoG.com and Itch.io when available, and pages like The big list of DRM-free games on Steam has been INVALUABLE for identifying games on Steam that can be downloaded and backed up. One thing I've been looking into is games that contain ROMs that can be played in emulators. Things like the SEGA Classics Collection just have the raw ROMs in the folder, but some other games they're embedded in the game data. I've found a few bits of custom python scripts here and there for extracting them, but it's been difficult tracking some of them down. For example, I found scripts to extract ROMs from Mega Man Legacy Collection and Mega Man X Legacy Collection but not Mega Man Legacy Collection 2 and Mega Man X Legacy Collection 2.
If there was a dedicated section on The big list of DRM-free games on Steam page specifically for ROMs that can be found in purchased games it'd make it easier to centralize all known ways to get the ROMs out. Maybe actually pointing to software for extracting the ROMs is against site terms, I'm not sure, but at the very least a list of games known to contain raw ROMs, or maybe even ROMs that can be easily extracted with an archive manager, would be a helpful resource.