Seems the in-game fps limiter always adds 1 to whatever it is set. For example, if set to 60 fps, in-game the fps limit will be 61.
A workaround I found was to set the MaxFPS in the Documents/Assassin's Creed Valhalla/ACValhalla.ini to a value that is 1 lower than what you want, for example, if you need 60 fps, set it equal to 59.
This value will reset to 90 if you go into the Options menu after launching the game though.
