Camera view distorted in build, but fine in game view within the Editor.

Good morning everybody, I think it's the second time overall I post here, but I really need some hint. Well, I updated from 2021.2.8f1 to 2021.2.9f1 and suddenly I have some issues with the main camera FOV when I build the scene (I know; being in full production now, I should have skicked to the LTS version, but I really wanted to implement AMD FidelityFX).

As you can see, the view in the build is distorted compared to the one within the editor:

The resolution is forced to 2k in the Player settings and of course I mantain the same one in game view for a correct reference. I simply don't get what's going on here, I didn't change anything in the project.

Thanks for any tips in advance!