I'm getting the above error when trying to connect to vpn given a .ovpn file. Usually this bug happens after an upgrade occurs and you haven't restarted yet. But I already did and the error still exists. I have tried reinstalling the openvpn (I'm using 2.4.7 on debian) and would not like to use this on docker.
Since getting this error when executing the command sudo openvpn file.ovpn often returns vague errors such as the one above, you can produce a more specific error when trying to import the ovpn file into NetworkManager instead.
After installing network-manager of course:
nmcli con import type openvpn vpn file.ovpn
Connect to the profile:
nmcli con up id vpn
Running this command would immediately show you a clearer error that is something along the lines of the org freedesktop networkmanager vpn plugin being unknown. Which is then solvable by installing the said plugin.
sudo apt install network-manager-openvpn
And that should do it.