I tried to install wifi-calling to avoid roaming abroad. And I've just realized that it does bypass the VPN.
To make GOS work with wifi-calling abroad, I had to install a VPN on a physical router. And connect GOS to my physical router.
And then, as if by magic, wifi-calling worked.
So it would be cool to prevent wifi-calling from bypassing the VPN. This would allow you to have an IP from the country where your operator is, and avoid roaming on wifi.