The king meter display works ok
There is no power to the wheel motor when peddling but there is power on walking mode
I can select all levels of power on the handlebar but it makes no difference to the power at the motor
The bike has been stored for over winter in a shed with no heating
That snippet of info actually tells us a lot .
If it works on walk assist then the controller is fine (it indicates the controller is working and powering the hub motor, controllers either work or don't work their is no inbetween ), the issue is most likely 99.99% the PAS sensor arrangement attached to the bottom bracket.
Show us pics of that area.
One suspects the PAS has been knocked out of alignment or a wire damaged.
Typically check the magnet disc is secure and can't rotate around it's axis by hand. ensure the magnets pass the sensor head quite evenly at a distance of 0.5 - 1mm.
By a £5 test meter to use for fault finding.
King meter tells us the system is a Lishui controller system.
As walk assist works we can rule out a controller mosfet issue and a motor Hall issue.