SOLVED
I can fully say that if you have changed your screen with a "replacement" from an unknown source then its the screen causing the issue. unplug the screen connector and plug in an external display and the critical update error will disappear and the TouchBar will work. It boots perfectly. plug the display connector in again and the error pops up again.
If you unplug the webcam connector on the display board attached to the screen then this will fix the problem with the error but you'll have no webcam unfortunately but the brightness control will work.