If the splashing is acoustically disturbing, you can remove the plug, otherwise I would leave it in.
The condensation water from the interior is pumped into the outer part, where it collects at the bottom (often referred to as a "sump" or "trough" in other areas of technology).
The fan has a kind of integrated water wheel, which flings the water from the sump/tub against the fins of the heat exchanger (or just "splashes").
Water has a very strong tendency to evaporate, and to do this it withdraws the necessary enthalpy from the fins of the heat exchanger (see
https://de.wikipedia.org/wiki...). On the one hand, this ensures that the water does not simply end up in the drain (or wherever the waste water from your outdoor part goes), but a) evaporates 100% and b) "incidentally" makes the outdoor part much more efficient.
If you have an ammeter, here's a practical experiment:
Hook up the Ulisse to an ammeter (e.g. a Shelly1PM or something). Let the Argo run for an hour until it settles down. Take a simple pump spray bottle for spraying water, and wet the outer part with 1-2dl of water (on the inlet side, not on the fan side). The system immediately regulates the consumption downwards, because it suddenly gets rid of much more heat via the outdoor part. Fogging in once pushes the consumption down by about 200-250W for almost a minute.
This splashing saves you electricity!
It would save more electricity if the water were distributed on the air inlet side, but the "water wheel" integrated in the fan saves a separate pump.