QUICK ANSWER
Check both water tanks and the cleaning tray/filter.
Roborock lists four main checks for a steady red Q Revo dock light: local voltage, clean-water tank, dirty-water tank, and correct installation of the cleaning tray/filter.

INTERACTIVE DIAGNOSIS
Clear the red dock warning
STEP 1 OF 3
Are both water tanks in the correct state?
Clean-water tank filled and seated; dirty-water tank emptied and seated.
Electrical warning
If the tanks and tray/filter are correct but the red light persists, do not open the powered dock to investigate voltage circuitry. Contact qualified support.