I'm not shocked in what happened to Cap in Endgame, ...20 years from now, And I'm sure Marvel Studios will be around, they could make a new relaunched Captain America movie. For the generation of movie goers and comic fans 20 years from now.
And things will be reset for a new young vibrant and exciting Captain America. New 3 movie adventure (Or TV series), evolving changing character arc, using new FX technology and with new great actors and sets.
And I hope I'll be alive to see all that new Relaunched Captain America series. But for now, the last 12 years of Marvel movies and Comic Books made Captain America a Great Character and an AAAA-plus Mega star and superhero! So, settle down, and live and love.
I just don't buy that he'd be happy in the past. It really ruins the character.
The only way it makes sense is that the actor is quitting and the studio is done with it for a while.