once you downloaded the game you can copy it into a pendrive, upload it into mega or whatever storage and use it. I don’t get why y’all get so held up at the fact that steam might stop offering infinite downloads. Once you have downloaded the game you are free to burn it or store it wherever! This is different from streaming music for example, since with music you never have a local copy you can work with.

so even if you download it once and think that you can now just transfer the game from one PC to another without an internet connection or without Steam, you can’t.

You can. I have several games where I can literally copy the game folder into another computer, press the executable and be able to play it offline. Terraria, vampire survivors, stardew valley, pathfinder: WOTR, Grim Dawn, AoE2… And more. I literally have “backup” zips of several path versions of grim dawn to play different mods because I’m too lazy to patch the game each time I want to replay different versions.

DRM free and actual ownership means physical

Once the game it’s in your system it’s as physical as it can get. There’s no difference of storage in your disk, a pendrive, an external drive or an optical CD. You give the example of GoG, there’s plenty games in steam that once “installed” have all the files in the game folder and you can easily move them.