This Seeking Tech article compares the Pro graphical mode of The Last of Us Part 2 to the Fidelity mode.
You can find the video comparison below:
The Pro mode is exclusive to the PlayStation 5 Pro. It renders at 1440p with a frame rate of 30 fps. PlayStation Spectral Super Resolution (PSSR) is used to improve the image clarity.
The Fidelity Mode renders at 4K with a frame rate target of 30 fps.
The Pro mode does provide a better image quality, although there is quite a bit of more visual noise. The trade-off is worth it, however, thanks to the improved frame rate, which is noticeable when aiming your weapon.