Brake light out- no power

good evening

I have a mk3 Octavia tdi Vrs on 2015 plate.

The LH brake light bulb isn't working and doesn't seem to have any power to it with the brake peddle pressed.

I fitted new lamps and even swapped over with the RH cluster aswell as plugging the RH cluster into the LH side but the problem still persists on the LH side. whilst checking these out, the RH cluster brought a fault up on the dash where as there isn't a peep from the LH side

Is there a separate fuse?

were is the main plug that supplies the rear lights?

isn't there meant to be a warning on the dash board?

any help gratefully received