The War Machine suit in the Super Bowl teaser is new and matches the leaked photos of a Mk 5 suit from before, albeit a little slimmer.
Could be a multitude of explanations as to why he has it. Could’ve been in storage ready to be deployed like the Iron Spider suit. Could’ve been a prototype. Maybe Tony built some emergency contingency program to keep building Rhodey suits in case something happens to him. Maybe there’s an automated War Machine printer.
Tony likes to be prepared.
Those are plausible theories (well, not the automated printer - lol), but IMO Tony would have kept Rhodey in the loop regarding any armor upgrades he was doing for him and given that, I still think Rhodey would have used the best of the bunch for the IW battle in Wakanda. They were fighting to save half the life in the universe, so you don't leave your big guns at home. So I'm thinking in Endgame either Tony gets back to Earth and upgrades him or there's a time travel angle involved.