Can someone explain how you play rdr2 for 6k hours? what exactly is he losing in game when stadia shuts down? so if he had played rdr2 on his pc, then stadia shutdown wouldn't affect him at all right?
Rockstar locks multiplayer to specific platforms, so if you buy a game on xbox and level up your character there, you can never use that same character on any other platform. In this way you are correct, if he had played on PC all this time then his game save would be in the PC platform cloud not the Stadia cloud.
The guy is a youtube/twitch streamer, so to him loosing this character probably feels like loosing his job.