I too have a problem! 2021 model convertible. Just checking prior to MOT, and the washers stopped squirting. Rear water tank is full - in fact I don't think it has ever been used since we bought the car (March 2020). Investigated the front tank, removed the sensor and filled that tank via hose. Washers now OK, but I don't think the front tank is being (or has ever) been filled from the rear. Fuses checked OK.
Car back together now, but will try another day to connect the front tank sensor manually so as to trigger the refill. Otherwise and suggestions as to how to check/resolve further? Maybe fit a fill pipe to the front tank?!