This video measures the frame rate of Marathon on the PlayStation 5 Pro.
The game only has one graphical mode, although you are able to switch between three anti-aliasing methods. The default anti-aliasing on the PS5 Pro is PlayStation Spectral Super Resolution (PSSR).
The frame rate measurement is done by using the in-game FPS counter.
You can find the video below:
As you can probably see, the frame rate remains at a locked 60 fps during gameplay during the tutorial mission. Unfortunately, there doesn’t appear to be any 120 FPS mode for the game on the PlayStation 5 Pro.