Thanks for the pointer, I will try that....as soon as I have repaired the network stuff that I somehow broke 15 minutes after I wrote the last text by trying to upgrade the host-debian system the webserver VM lives in.
But yes, its a problem with other devices, but actually not with the windows gaming pc that is connected via cable, only Wifi devices seem to have that problem. I actually checked if the swap to the guest wifi (because for some reason it has better connection?) and it doesnt, so its at least not that
Also thanks for this advice, this seems easier than I thought.