> That's not in any way what gog says.
Jesus Christ. It's exactly what GOG says. Compare https://www.gog.com/en/news/bgog_2022_update_2b_our_commitme...
> 1. The single-player mode has to be accessible offline.
> 2. Games you bought and downloaded can never be taken from you or altered against your will.
> 3. The GOG GALAXY client is and will remain optional for accessing single-player offline mode.
> Having said that, we believe that you have the right to make an informed choice about the content that you choose to enjoy and we won’t tell you how and where you can access or store your games. To make it easier to discover titles that include features like multiplayer, unlockable cosmetics, timed events, or user-generated content, we’re adding information about such functionalities on product pages. In short, you’ll always know.
If you want to play multiplayer HoMM3, you can. That's how the game was commercially released and it hasn't been updated to add DRM.
Modern releases DRM the game as a matter of course, and GOG defied their user base to say that that's fine with them. Do you want to play with your friend? You need an internet connection and multiple accounts registered with the vendor.
For a concrete example of Galaxy being the DRM implementation, the Gloomhaven executable you can download from GOG has the button to play multiplayer disabled. It will still work if you get around that - the functionality itself doesn't check anything. But the executable will only enable the button if you start it with Galaxy running and logged in to an account that, according to GOG, has purchased the game.
That doesn't sound like "digital rights management" to you?