Of course, this doesn’t mean that Moira won’t receive a wink, nod or mention during the events of X-Men: Dark Phoenix.
All it really tells us is that Moira won’t be joining the ensemble on this adventure.
Charles’ long-dormant romance (although at this point, it’s really little more than a crush) has informed much of his characterization since James McAvoy stepped into the role in X-Men: First Class, so for someone like Hank McCoy (Nicholas Hoult) or Magneto (Michael Fassbender) to mention her in passing would make a certain degree of sense.