Can you name a big single player game from before 2004 that required online DRM?
Because you originally couldn’t play single player HL2 without internet. They slowly backed off the DRM but it wasn’t like you needed to register once and could play forever. You needed Internet to play single player.
I don’t remember needing a constant internet connection to play hl2. I just remember needing it after the initial install. 20 years was a long time ago, so I don’t remember if it was the first single player game that had to be activated online first to run or not. I remember a lot of cd keys and ban type stuff for multi-player games pre hl2, but I don’t recall any single player ones.