Deadpool & Wolverine establishes that the Merc with the Mouth resides on Earth-100005, the same world inhabited by the X-Men and the reality where Wolverine died in 2017's Logan.
Early on in the threequel, we learn Wade Wilson used Cable's time-travel device to visit Earth-616 and request entry to The Avengers. Happy Hogan politely turns him down and the anti-hero later reveals he destroyed the device upon returning to his own timeline.
The TVA was aware of what Deadpool did but chose not to intervene...at least until now. Loki made it clear the organisation's reach is pretty much endless and we discover here Mr. Paradox has been tasked with overseeing the death of Earth-100005.
He explains how every reality has an "anchor being," a person of such importance that, when they die, so does their world. In Earth-100005's case, Logan's heroic sacrifice sent shockwaves through his world and, in roughly 2000 years or so, it will end.
Paradox doesn't wish to waste time and has ambitions to take charge of the TVA. That's why the villain has created a Time Ripper, a machine which can wipe a timeline from existence immediately. Knowing Wade could be a problem and suggesting one of his higher-ups wants the Merc on Earth-616, Paradox offers him a place on the Sacred Timeline.
Deadpool refuses when he realises it means never seeing his friends again and sets out to find a new Wolverine to replace the one who died saving X-23's life. Alas, it doesn't work like that and both heroes are sent to The Void.
It's important to note anchor beings are not the same as nexus beings. It's been explained that they are an entity with the ability to affect the probability of an event and create Nexus events which wouldn't otherwise happen; in the past, the TVA pruned their timelines. It's confirmed that this movie takes place after Loki season 2 when he mentions Earth-616 is the Sacred Timeline and suggests Earth-100005 is one of an infinite number of branches.
As for Earth-616's anchor being, rumour has it that it's Tom Holland's Spider-Man.
When the movie ends (and we'll be back with a full explainer later), Deadpool and Wolverine heroically stop Cassandra Nova from destroying the Multiverse with the Time Ripper - which would have left only The Void - and Logan's heroism saves Earth-100005.
Wolverine remains in that reality - where he'll presumably get a second chance with the X-Men - and as Hunter B-15 explains, the timeline is now thriving, meaning Deadpool's original plan worked. So, the Fox-verse is very much alive and well heading into Avengers 5.
This surely means we're getting something along the lines of Avengers vs. X-Men as an Incursion would bring Earth-616 and Earth-100005 together in a way which gives Marvel Studios an excuse to have these characters meet.
While we still don't know whether this reality is the same one we saw in The Marvels (we'd assume it isn't as the events of Logan played out on Earth-100005), then there may need to be a retcon somewhere along the line to make a possible clash work. Also of note is the fact Wolverine joins Wade's reality with X-23 by his side; she was in The Void and it's strongly hinted that she's Logan's Laura, meaning she must have been pruned at some point and is now similarly restored.
Ultimately, Deadpool & Wolverine is pretty standalone so whether this is the end of the story or there are plans to add these characters to the mix in the next Avengers movies remains to be seen...