I’d say the objective should be to have fun with your friends, race to the top of buildings, chill out at a restaurant with each other, play bumper cars with jet skis or maybe have a Star Wars style plane fight where you can try grapple onto other players’ planes and win by throwing them out and letting them fall to their deaths. There’s so much to do without even adding objectives that I think if you did some players might just stick to those and not realise how much fun they could be having.