Hey ,
We have an article here explaining how cross play will work in EA Sports FC 24:
https://www.ea.com/en-gb/games/ea-sports-fc/fc-24/news/fc24crossplayupdate?setLocale=en-gb
I think the part you're specifically looking for is:
- PlayStation 5, Xbox Series X|S, and PC versions being able to play cross-platform
- PlayStation 4 and Xbox One versions being able to play cross-platform
- Switch will be excluded from any cross-platform play.
However, every version of EA Sports FC 24 comes with dual entitlement. So if your son downloads the last gen version of the game, then he'll be able to play with his friends. (It shouldn't have any effect on his UT progress either). You won't need the Ultimate Edition for that.
To put it in simple terms: Yes, it's possible, there's just a hoop he'll need to jump through.