Pfeww… got it solved. Seems like Proton did do some kind of killswitch and could disable it with this.
Thanks for your support anyway!
3. Disable Kill Switch if you have uninstalled the app
The Kill Switch can be easily disabled from within the official Linux app, but this will not be possible if you uninstalled the app without first disabling the Kill Switch. This may result in your system being unable to access the internet. To remove the Kill Switch after the app has been uninstalled:
a) Identify Proton VPN connection names by running the command:
nmcli connection show --active
This will display a list of all your system’s active connections.
b) Look for any connections with the pvpn- prefix. This usually includes pvpn-killswitch and pvpn-ipv6leak-protection, and may include pvpn-routed-killswitch. Delete all these connections using the following command:
nmcli connection delete [connection name]
For example:
nmcli connection delete pvpn-killswitch
c) Re-run the following command to verify that Proton VPN connections have been deleted:
nmcli connection show --active
If any Proton VPN connections remain, delete them as described above.