Believe it or not the title was in place long before the title of avengers endgame was set in stone as a confirmed title actually you could say the studio had been teasing the title since avengers age of Ultron what we dismissed as throw away lines have been leading you to the last movie all this time let me jog your memory a bit
“That up there,” Tony Stark states, referring to the events of the first film when the titular team withstood an alien invasion of New York. “That’s the endgame.”
Then it gets said again by Doctor Strange in infinity wars for shadowing the visions we saw in the first movie where you see half the avengers dead that’s the endgame Meaning end of the avengers end of a brilliant franchise
That’s my theory but I want to hear yours below sound off as always in the comments and for now I’m Luna wolf 🐺 signing off