The first couple minutes should show the decimation of the universe because of the snap. The aftermath of the famous snap.
What does life look like? How are people reacting? Show how depressing and chaotic things became. Show how things changed and the destruction it caused.
This can be done in 1-2 minutes before showing Tony Stark & Nebula returning to earth a couple days later or so. Tony and Steve Rogers are reunited, shake hands, express their shock, sadness, disbelief, brokenness.
It is clear they have no clue what to do now.
Opening titles / title reveal
Fast forward several years later....
the planet is dramatically different than prior to the snap, and the Avengers have all but lost hope before something happens and the movie’s plot begins....
I think this is how it should open because it reveals the true effects of the snap and the harsh and horrifying reality of it. All hope is lost!