As above, the radio on my 2003 TD6 is lit up and shows the screen with the list of option such as on board computer, set-up, off road navigation, and I can scroll to each option with the turn knob, but neither knobs work when I press them?

Is this a common fault please??

I would let the satnav drive unit power down, disconnect and check there is no corrosion on the pins, or the connections are seated correctly as it sounds more software than hardware related and that screen is controlled through the satnav drive. Current Fleet:-
2018 Discovery 5 3.0 HSE
2021 Ford Ranger Wildtrack
2019 Ford Mustang Bullitt 5.0 V8
1993 Defender 90 200TDI Pickup

Gone - not forgotten
2016 L405 4.4 SDV8 Vogue SE
2012 L322 4.4 Westminster
2004 L322 4.4 V8 Autobiography LE
2000 P38 RR 4.0 HSE (ex Clarkson test car)

Update, went out to the car Sunday morning and all was fine? Am guessing the cold weather maybe?