F138 on Miele indicates Waterproof has been activated because of water in the bottom tray. Shut off the water supply and request a leak inspection.
Stop the water supply and isolate safely
The manufacturer documentation links F138 to an internal leak. Turn off the faucet if you can reach it from a dry area. Disconnect using the designated point only when it is safe to do so; if there is water near electrical connections, ask for help without touching the plug or stepping into the puddle.
Continuous pump operation may be part of the protection. Note whether you hear it, but do not keep the unit running to check how long it takes to stop.
Clothes trapped and internal water
Miele refers water removal from the base and the repair to its service team. Do not tilt the machine or open panels to dry it out and clear the warning. If you need to retrieve laundry, use only the emergency procedure in the manual when its conditions for cold water, safe level, disconnection, and stopped drum have been verified.
Record the water location and when it first appeared from outside the unit. The leak-finding guide lets you describe those observations; the internal source requires diagnosis.
The fact that water is no longer visible on the floor does not confirm that Waterproof was triggered by a cause that has already been resolved.