After I did the trick with reinserting the DW1560 card a few times, I need to sum up that this doesn't work any longer. Even Ubuntu loaded from USB freezes immediately after I installed the correct drivers.
Replaced the DW1560 card with the original Killer 1535 card, this results in no freezes, but, of course no wifi too.
I do have a spare TP-Link TL-WN821N V4 USB wifi stick, with an old RTL8192U chipset which I got working using drivers from
here, but this can't be a solution.
I looked for an DW1560 replacement, I got the first one from Aliexpress, but shipping takes very long and it isn't even cheap at 40$. In Europe I would need to pay 60€ (not $) for it.
Is there a newer Dell wireless card I can try? Newer than DW1820 and DW1830 as these cards are hardly available too.
Thank you! All of you! For making this fantastic notebook even greater!