Thank you, John, for your answer.
So, I understand correctly, that it will not matter whether there is a cartridge in it nor will it matter whether it is original Epson or third party cartdrige? I do NOT have original Epson cartridges to insert if the process notifies about trouble.
One more "little" problem: This printer does not accept thick paper (160 g/m2) in the paper cassette. It will eject the paper and say "paper jam". (How does it find out about paper weight? can I disable that?)
An alternative would be to use the rear tray, but here it will not do duplex printing (Obviously, thick photo paper does only have ONE shiny side, and the back side should not be printed on. I understand).
But I want to print little broshures in duplex mode, on 160 g paper. My older printer WF7525 does exactly this without any problem, although it does it slowly and it may overheat.
The WF5620 does already have firmware GM09GC installed. But the Version GM09GC that you deliver is a modified one, correct?
Somewhere I was reading that Epson uses Linux software open source. Consequently I assume there should be a way to access the necessary settings (paper weigth, duplex printing) and change them. Can you please give me hints on how to do that? You may as well contact me by email or PM. Thanks again.