Hoyhoy.
PROBLEM..Interior fan only operating on speed No4.
REMEDY.
The usual reason is a resistor, pull the glove box out to gain access & then have small hands.
Don't pull all dash apart like me did, the resistor from VW = $77.00.
Told by VW spares man that it was quiet common as it is put in there to keep cool & gets all the condensation from the air conditioning.