Spider-Man: Far From Home was a good time but Marvel and Sony made an odd decision to release the first trailer before Avengers: Endgame, which had fans speculating about everyone's fate (that was probably intentional). If fans have revisited that first trailer, they'll notice how we see Peter in the Homecoming outfit in certain scenes when he's actually wearing the Iron Spider armor from Infinity War and the upgraded suit in those moments.
Apparently, they didn't want to spoil Avengers: Endgame or the fate of his Iron Spider armor, even though the studio didn't seem to care about Spider-Man still being alive. So, without any other option, they decided to CG in his Homecoming suit during certain scenes so that nothing Avengers: Endgame-related would be spoiled.
Julian Foddy, the film's visual effects supervisor, confirmed this during an interview with Before and Afters:
"They didn't want to reveal that Spider-Man survived Infinity War and his possession of the Iron Spider suit on Earth would have given that game away."
Once Avengers: Endgame started screening, Sony and Marvel decided to not hide anything for the Far From Home advertising, aside from Mysterio actually being the villain. This must have been quite a relief for some, though they probably should have waited a bit longer so that they wouldn't have to go through all that CG effort to hide some spoilers.
Spider-Man: Far From Home is now showing in theaters.