Question about Hoymiles Inverter HMS-800-2T Microinverter

The Hoymiles HMS-2T inverter is the successor to the Hoymiles HM-800.

The HMS-2T has a new plug-in system and integrated WLAN capability, eliminating the need to purchase an additional external DTU. The HMS series can handle higher input currents on the DC side. It is also cascadable, but cascading can only be done on the AC side of the HMS series, not with the battery plugs/sockets. Both models have two independent MPPT (Maximum Power Point Trackers), which means that the output of the solar modules is optimised independently of each other.

Good morning Mr Stoller.
The question regarding the Y-plug has been resolved. I was able to clarify that it is not recommended by experts!
But the other questions are still open.
Thanks and regards Werni

Hello Mr Stoller
Thank you for the detailed answer. SUPER!
I still have this question:
What happens if I connect only one module (420wp) to the HM-800 instead of - as intended - their 2
Will it produce the 420wp or will there be a loss due to the 2 MPPTs?
Would it be better/smarter to use an inverter with 400 or 500W or perhaps short-circuit the free DC connections for the 2nd module with a Y-connection?
Thank you for the clarifications!
F.G. Werni