If this is the case which it can be as kill switches by VPN apps and services in their GUI apps are not fool proof yet on Linux at-least, then the best way to use a VPN on Linux is the way I describe it in my community post here: How to best set up & use a VPN with WireGuard on desktop Linux
Yes, this should be the case. It’s clear now. That’s what I was getting at but the way you wrote it implied that you were expecting something else.
The best VPN with a GUI on Linux (on the officially supported distros) that does work ensuring of leaks and whatnot is Mullvad. Others can be finicky on Linux.
I hope I am clear now too.