2 main possibles…..as F21 is motor circuit fault
Brushes worn in motor
or
Faulty module.
You will need to enter the test programme to clear the fault display.
IIRC on this model , its selector knob round to the 6 o’clock positiion. Finger on the spin speed selector button and turn the selector one click clockwise – release the button and you’re in the test programme. Now , the F21 display may not go straight away so you may need to turn the machine back off and repeat the process.
Then check the motor brushes !!