Hot Take:
the marketing makes a game OSR.
The slightly spicier hot take:
OSR games tend to be structured around an imagined (mostly by designers who were not born yet or not playing ttrpgs at the time) play style supposed (by those same designers) to have been dominate in the “early days” (dates vary wildly) of the hobby. They are all focused on a single game (DnD) while ignoring all of the other early systems and inovations that share those dates (traveller, Runequest, etc).
That said I like some”OSR” games a lot and some of the folks in the “scene” are fantastic people but at the end of the day most of it is just DnD of some flavor or another.