That has to be illegal right? Like building a mod for a game is fine but if you charge people for the mod for that game its illegal in most cases. This is effectively that.
Heavily depends on how the mod interacts with the game. If it does not use anything that's from the game, selling stuff becomes against ToS at the best and illegal at the worst
While it may not use any assets from the game, it sure as hell uses asstes from Nvidia (?) that are required to enable DLSS3. But I don't know how they are licensed and if a sale is allowed...
Unfortuantly his code doesn't act independently of its own accord or through software that has permission either. Unless he has a deal with Rockstar (doubtful) they can claim this as a violation.