Since a few months, I can’t connect to the internet anymore when on an ICE train in Germany. (My config is a pretty plain KDE & Networkmanager.) Does this work for you? If yes, did you do anything to get it to work? I’m assuming that it’s a NixOS specific DNS issue, because noone else, not even Linux users, seem to have this problem. (Android always works.)
I can connect to the Wifi WIFIOnICE, that’s not the issue. Some months ago, there would be a dialogue that would automatically pop up in Firefox to connect to the internet. This dialogue doesn’t appear anymore.
it’s likely there is a captive portal to get Internet access over the wireless connection. If your web browser doesn’t redirect you there, this could mean:
check you are not using a custom DNS server
check your web browser isn’t using DNS over TLS/HTTPS
I can also highly recommend captive-browser. It works even with a fully encrypted networking setup and does not mess around with your system’s dns at all.
Alternatively you can also just set up a special DNS zone for whatever URL your browser chooses to detect captive portals, and make sure that isn’t sent through your VPN interface or to an encrypted DNS provider. Here’s Firefox’ docs on that: Captive portal detection | Firefox Help