You really thought it was that easy?
It would seem that it's not enough to officially announce mutants in the Marvel Cinematic Universe for the studio to be able to introduce the iconic X-Men. According to Devin Faraci, former editor-in-chief of Birth.Movies.Death. and current co-host of Marvelvision, it is an issue of copyright.
Faraci said that 20th Century Fox's contractual obligations to actors in the X-Men franchise have carried over to Disney and Marvel and are in effect until 2025, meaning that the studio will not be able to recast, announce or start a production of a film that includes someone (if not everyone) from the Fox X-Men franchise.
This does not prevent Marvel from teasing mutants and introducing new mutant characters – it would seem that exactly that happened to Ms. Marvel, a character that is initially owned by the studio. Kamala Khan seems to be Marvel's first mutant – and now that the introduction was made, it's likely she is not the last one.
But some time has to pass before the iconic characters like Wolverine and the like can be properly introduced into the MCU. The year 2025 is going to mark the end of Phase 6, so it would seem that Phase 7 is the earliest we're getting X-Men in the MCU.
Despite being pretty disappointed about that, fans still have some hopes left.
"Not going to lie, if this is true, I will be pretty disappointed. That being said, this does leave the door open for Fox X-Men cameos in Secret Wars – and probably makes that more likely now." – /Vilarf
Given that Phase 5 and Phase 6 already seem pretty stuffed, there are possibilities for the MCU future that are already open.
"I'm starting to think our core X-Men team will come from a different universe and will end up mentoring the younger Mutants emerging in the 616 timeline." – /ViggieSmallss
The mutants have been seemingly confirmed in the finale of 'Ms. Marvel', when Bruno revealed to Kamala that she had a "mutation" in her genes – all this to the iconic '97 X-Men soundtrack.