Screen Rant is speculating that Avengers 4 will basically be The Butterfly Effect (spoilers?)
Traveling back in time through one's own memories, basically.
https://screenrant.com/avengers-4-theory-time-travel-memories/2/
This article mentions the above, but shows a bit more:
https://www.inverse.com/article/47525-avengers-4-spoilers-theory-antman-wasp-time-travel
Oh and I don't think anything can be "spoilers" for this movie considering the first person in the cast list is a spoiler, and the full cast list includes so many other "dead" Marvel characters that were culled by Thanos.
Plus, we all know none of those are staying dead.