I would not add any cleaning agent. The water is only brought onto the floor with the microfibre cloth at the back of the unit, (spread).
The water only evaporates and is not absorbed. With detergent in the water, the water will evaporate and the detergent will remain on the floor. This can lead to streaks, stains and greasy as well as slippery floors.
Not recommended in my opinion.
Greetings

Only water or special cleaners for floor mopping robots such as (Google) "botClean floor cleaner liquid" are really officially approved, and there are also a few others from third-party manufacturers. So far "officially". Unofficially and at your own risk: I myself sometimes mix in a thimbleful of cleaner for ultrasonic cleaning devices. It is important that the agent a) is really liquid (does not have to be dissolved in water first) and b) does not foam. (Which makes soapy water unsuitable from my point of view).