If a video was recorded at 120hz, would Infuse player play it at 120hz on iOS? (for the iPhone 13 pro and iPad Pros)

Basically what the title says.

I believe so yes.

However, Apple devices have limited support for HFR content, so playback quality may vary based on the specs of the actual video being played.

We did include a few improvements for HFR videos back in the 7.3 update.