Watching it, I thought "IF it will get no open matte version, why don't we replace the flashbacks with the open matte version?"
From what I read on Imdb, the IMAX version is 1.90:1 and they don't add "on some scenes", so fully 1.90:1. It will probably pop up at some point on HBO Max when they get on board the IMAX Enhanced train. I don't see the point of a partial open version just on the quick flashbacks.
I got the "if" part, but even so, the flashbacks are too quick, as many as they are, to bother doing such a thing.
Quite a lot of people like it, so us?
That was just a joke, to each their own.