I tried both Mullvad and Mozilla VPN and when I do a dns test, both are still using my ISP’s DNS instead of the VPN’s. This only happens on my Arch systems, works fine on my phone.
EDIT: Turns out these VPN clients depend on systemd-resolved in order to change your DNS. Enabling the service makes it work properly. A bit scary that they don’t give you a warning that you’re leaking DNS if you don’t have systemd-resolved enabled.
Yes I am using Network manager and it writes to /etc/resolv.conf. The entries in my resolve.conf all just point to my router IP. Is the VPN supposed to add entries into this? I remember it used to work automatically. I never had to manually change resolv.conf before.