You could make different player’s in-game clocks appear slower or faster, but you obviously couldn’t affect the players’ actual subjective clocks, so you obviou

You could make different player’s in-game clocks appear slower or faster, but you obviously couldn’t affect the players’ actual subjective clocks, so you obviously couldn’t do any of the interesting things like the twin paradox, unless the entire in-game simulation was sped up significantly and you could do something interesting with in-game characters aging at different rates.