While connected to the Internet launch each game once, switch Steam to offline mode then launch each game in offline mode and see which ones boot up and write them down.

Note: Those that do launch may require to connect to the Internet at some point.

Alternatively go to each game folder while not connected to the Internet, run the game from the exe and see which ones boot without requiring Steam.

you could also try buying games on another platform without DRM, if available for your choice of game.

Not having internet puts you in a niche demographic. So I wouldn't expect a lot of thought being given to your circumstances by web based platforms. As a result you're probably going to need to manage that yourself.

Maybe you need to make a spreadsheet, or find someone in your boat who's already done the work. Because while you're in a niche demographic, it's a lot more than just you, and this may be a problem other people have already solved.