Just for fun, this is the list. I considered all 2/3 timelines and the parallel universes too: "Deadpool" and "Logan".
Definition of "X-Man" in the movieverse, as hinted by the movies:
Mutant operating as Xavier's assistant/bodyguard, teacher of Xavier's "School for Gifted Youngsters" and agent of a special stryke force using specific tech (uniforms, Blackbird). Point #2 optional.
1- Xavier (codename "Professor X" used later, when he wasn't an X-Man)
2- Lehnsherr/Magneto (codename used as X-Man in 2023)
3- Mystique
4- Havok
5- Banshee
6- Beast
7- Cyclops
8- Storm
9- Marvel Girl/Jean Grey (codename presumably used long before the movie "X-Men")
10- Wolverine/Logan (the name "Logan" used as X-Man in 1973, during the movie DOFP)
11- Rogue
12- Iceman
13- Nightcrawler
14- Colossus
15- Shadowcat
16- Angel (wearing an uniform only on promotional material)
17- Bishop
18- Blink
19- Sunspot
20- Warpath
21- Quicksilver (first time as X-Man in 1973)
22- Negasonic Teenage Warhead
23- Caliban (ever if never explicity stated, he acted as X-Man in many ways in "Logan")
24- Deadpool
25- Yukio