If you can find them and the new Xbox is backwards compatible start with Fallout 3 then New Vegas (personal favorite) then jump on fallout 4. You will probably be camped out on fallout 4 for awhile, I still regularly play and I've had it since release day
Fallout 76 is better then advertised once you get into it. I will only play solo because I hate playing with other people, but it does have multi player missions that look cool. They have also added a bunch of new content that I have yet to touch.
I have the orginal 2 for PC, but they are from 98/2000 and are SLOWWWWW going to the point of boredom
I'm playing Elden Ring right now, and I have the new Horizon game still in the pkg.