Hey, I really like the design of your App, but was unable to use it as I always had the state "no internet".
I couldn't understand why only this Flatpak App couldn't access the internet.

The App has the flatpak sandbox network permission, so that shouldn't be the problem.

I then used Wireshark to try to find the issue and stumbled upon this. A connection to 1.1.1.1 on Port 53 (DNS) is blocked by my network gateway. This is intended as I have a local resolver and don't want other DNS Servers to be used on the network.

The allowed DNS Server is set as the system / network connection DNS Server. It seems the App has 1.1.1.1 hard-coded and therefore ignores the system-wide DNS setting.

When I temporarily disabled the external DNS filter on my network gateway, the application worked normally.

As far as I can see, the App should just use the system-wide DNS setting, like any other Application does.
It could also be that the App uses a DNS Request to 1.1.1.1 to perform the internet connectivity check itself, then maybe using ping one.one.one.one or nmcli networking connectivity (on Devices using NetworkManager) instead would be less error-prone.

See here under "Networking Control Commands" for the possible return values of nmcli networking connectivity.

Thank you very much!