In modding everybody at least once mentioned verifying game files. It's a process when the launcher (Uplay or Steam) will check game files and if they aren't original then it will download them again, so it will restore game files to their original state.

Far Cry 6 note

Since Ubi changed patching system in FC6, there is one more step you need to do.

It's required to delete two files after you verify game files, so go to your game install folder and then go to data_final/pc/ and here delete files patch.dat and patch.fat.

More here:
Uplay: Verifying game files in Ubisoft Connect PC
Steam: Verify Integrity of Game Files
Epic: How do I verify game files in the Epic Games Launcher?