do you have an example for a game that accepts circle as the back button? I didn't try in every game I played on PS1, but at least the UI will usually tell you to press Triangle. same on PS2. and on PS2 I know miltiple games where circle does not work. I play more PS2 stuff than PS1 stuff in recent years, which is why PS2 examples are fresh in my memory.
But I think I still know some PS1 examples. Most Sony published games will only accept Triangle and stuff like God Hand on PS2 will also only accept Triangle. same with Shadow of Rome I think and Time Splitters 1-3
those are the ones I am 100% certain about