As far as the world is concerned, Magneto defeated Apocalypse based on news reports at the end of that movie. Just like as far as the world is concerned Mystique saved Nixon and changed the tide for for human-mutant relations for the better in Days. Without any help from Xavier (nor Beast nor Jean nor Cyclops nor Storm nor Nightcrawler) for the former.
Without any help from Xavier (nor Beast nor future Logan) for the latter.
So why is Xavier on the cover of Time? Why is Charles a superstar? Why is he a Nobel Peace Prize winner? And if the answer is that Professor Charles Xavier did something special between the end of Apocalypse and the beginning of Dark Phoenix, why is all that interesting stuff happening in between movies?
Creative Writing 101: Show, Don't Tell.