I want to setup NextDNS on my devices as I like their ad blocking and other features, but I also use ProtonVPN and know that's a problem. ProtonVPN doesn't support CustomDNS very well and only support IPv4 instead of IPv6, which is the better option. I know they prefer you use their DNS service, but I think the pros of NextDNS outweigh the cons for me. Is there a better way to set NextDNS with ProtonVPN?

What platform are you on. This url covers most of them. https://protonvpn.com/support/custom-dns

At the moment, Windows.
I just looked at the Proton Support page and it says for Windows, it will take the IP adress. I know I don't have much of a choice, but using adding the IP address better than the IPv4 or IPv6 address?

The catch with putting NextDNS's IPv4 addresses into Proton's custom DNS is identification. Plain DNS to NextDNS only reaches your configuration through the linked IP, and behind the VPN that is Proton's exit IP, which is shared and changes with every server. So the filtering and logs won't reliably be yours. Custom DNS in Proton also only works with NetShield turned off.

What works better on Windows is encrypted DNS that carries your config ID itself: the NextDNS app, or the DoH address from your NextDNS setup page (it ends in your config ID) entered in the browser. That traffic just goes through the tunnel like any other HTTPS, so the VPN and NextDNS don't fight over it. Worth checking with a leak test afterwards that queries actually show up in your NextDNS log.

Ok, I'll take a look at the NextDNS app. Thank you!