https://www.gog.com/game/airline_tycoon_deluxe https://www.gog.com/game/airline_tycoon_deluxe https://www.gog.com/game/world_of_goo https://www.gog.com/game/wo

https://www.gog.com/game/airline_tycoon_deluxe https://www.gog.com/game/airline_tycoon_deluxe https://www.gog.com/game/world_of_goo https://www.gog.com/game/world_of_goo (was also free on Epic Game Store a while ago, plus in a million different bundles) for example. The games used as tests seem to be lower end indie titles that can be found DRM-free (because you don't also want to have to work around that)