Shut down.
Hold Volume Up.
Press and release the Power button.
Keep holding Volume Up until the Surface logo/UEFI appears.
Test the keyboard there.
Test Caps Lock in UEFI
If the Caps Lock/Fn indicators still don't respond in UEFI, Windows/drivers are very unlikely to be the cause.
That would strongly suggest the keyboard/keyboard controller or its connection is faulty.
Check whether the keyboard works before Windows loads
If it works normally in UEFI but stops working once Windows starts, then we should investigate Windows/firmware/driver/software.
If it doesn't work even in UEFI, I'd focus on hardware/service, rather than repeatedly reinstalling drivers.