If the Xiaomi Robot Vacuum S40 cannot remove stubborn stains while mopping, manual cleaning can be required for certain tough stains.
For your reference, here is more information about cleaning stubborn stains:
1. The mop module uses consistent pressure and a damp cloth to wipe the floor. While effective for general maintenance, it can not provide the scrubbing force needed for hardened or greasy stains;
2. For tough stains such as dried liquids, sticky residue, or grease, manual cleaning is more necessary to achieve better cleaning effects. In such cases, it’s recommended to pre-treat the area with a suitable cleaner or wipe it manually before or after the robot’s cleaning cycle.