Basically what the rest said. It could be due to the comics division waiting to see what’s going to happen on WandaVision and Doctor Strange before they proceed, or they could just be keeping him trapped in Limbo as the Avengers office is wont to do instead of just giving him back to the X-office already.
Oh, and then there’s this
61F48CD9-DCFB-4D9E-AD2A-9DCBC7CF6EB8.jpg
I have no idea if he’s going to show up in it, or is just on the cover.
You missed the X-Factor one shot by Peter David, The Quick and the Dead. I can’t say it really clears much up, but you do see him becoming really fast again instead of only time jumping and crystal huffing.