@ikoz I think i have found the solution. After allowing outgoing traffic to 188.166.175.79 port 5001 the notifications seem to work. lsof, netstat and a little bit more googling helped me. After disabling ufw; lsof and netstat were showing the IP and port after a notification came in. Port 443 is needed, too. Unfortunately logging with ufw does not work, but who cares, i didn't need it. Thanks for pushing me into the right direction, this warning app could save a life.

@kugiigi When using QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling); it looks the same on phone and TV. That's nice, but i think i will stick with units.gu(). I've tried it and, so far, it works nice. I saw there are problems, but that's not the fault of my app.

@wynn1212 You're the best . TBH i was hoping you would do it, because you faced the same problem. Maybe there will be a real solution soon .

It's been awhile since I've used the installer, it surely has changed since then. Thanks for the hints.

A pity. Than i'll have to deal with that and re-enable it after every call.

@Inali Thank you for the effort, maybe this site helped a little bit. The solution i've found is a simple: sudo ufw allow out on waydroid0 to any. I was (and still am) confused about the 2 devices and how they "work" together. Now that i know which interface to deal with i can, of course, precise this rule, but i have another (Android-) firewall in the waydroid container that can handle this.