I don't have Mad Max in my GOG library, but there are no complaints about DRM in the reviews or on its forums, and usually GOG folks will complain in one or both of those places whenever something's foul, including multiplayer (as they should). It's what got Hitman (2016) pulled from GOG, as while it's technically playable from the start of the story through to the end, it requires online connectivity for its most compelling features beyond that. As for Saints Row IV, I just installed it from the installer executables and launched it with my internet completely disconnected, so if that was a faux pas for that game at one point in time, it has since been corrected. It does require Epic Online Services for multiplayer even though previous versions of the game supported LAN, but I only have Re-Elected in my library. Others, I think, got Re-Elected added to their library if they had the legacy version.

Also, both of those games are stretching the definition of "modern" at over 10 years old.