Shift Lock is a setting available for PC and Mac only. Shift Lock is basically a cheaper way of using 1st Person Mode, as the player is locked in the position their mouse is facing. Now, I've tried a couple scripts to prevent the player from using Shift Lock (but not 1st Person) and none of them work. If somebody could please take me on the right way, that would be very helpful. Thank you.
Open explorer and properties, scroll down in Explorer till you see StarterPlayer.
Click on StarterPlayer and then untick EnableMouseLockOption in properties.