If you’re looking for the answer to how to get Gnome to connect to your OpenVPN using OTP, then you’re going to come to a dead end.
There’s been an outstanding issue logged on Gitlab for over 3 years (to date) that wants this facility fixing.
https://gitlab.gnome.org/GNOME/NetworkManager-openvpn/-/issues/12
It’s frustrating because we have mostly Linux users. The few macs and Windows users are all right, they get the OTP prompt. Even Android works as it should, it’s only Linux that needs fixing.
I tried the workarounds from the comments and none of them worked for me.
For now, you’ll have to satisfy yourself with using the command line.