In Endgame they explained how time travel works in the MC universe. And we have seen how it works in X-men universe 2 times (DOFP and DP2).Unlike the MCU, in X-men universe you can change future by changing past. So these two have completely different rules of explaning time travel.
Now that marvel has all the rights to the characters, we will see them as part of one big multiverse. And two universes following different rules of time travel doesn't make sense. Of course two different studios didn't know these characters are gonna share the same multiverse in the future.
I expected to see some kind of little explanation in D&W but they choose not to touch it. And I am now Okay with it. As its already confusing and general audiences don't care. I AM JUST HAPPY I WILL GET TO SEE cyclops, spidey, cap, wolverine in one movie. Maybe not in Doomsday but definitely in Secret wars.
One thing they’ll never explain, and I’m Okay with it