thanks, at least for the first point, those “Fritz Box” Routers are somewhat usual in german, I got my own to have more control over my network…and it does indeed support NAT loopback, I think that is what I had to configure in my previous IPv4 Setup for everything to work. For the rest…I will have to do some research. Although, my IPv6 address starts with 2a02 and is indeed reacheable from the outside, so apparently that is a thing

Also thanks for this advice, this seems easier than I thought.

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