The First Class tag line pretty much spelled out endgame right off the bat:
“Witness the moment that will change our world.”
DoFP doesn’t have one and doesn’t need one because that tag line works for both films. Unless you wanna make the DoFP tag line “Witness the moment that will change our world…again.”
The “moment” is Charles meeting Erik.
Plenty of people out there also pointing out that it kinda looks like Charles and Erik are holding hands.