NextDNS, ProtonVPN, and iPad Pro

I didn't have much luck with the NextDNS app and ProtonVPN on iOS.  TBH, I didn't really pursue it either.  I'm using ProtonVPN w/ AdGuard Pro.  With setup I can filter locally in the AdGuard Pro App, adding blocklists, etc, and I use NextDNS (DoH) as the upstream resolver.  This setup works well and gives lots of control at the device level.  I will say, currently AdGuard is having an issue with the transition from WIFI to cellular, but once that's sorted (again) then all will be good.  I really rate this setup, and with AdGuard Pro you can block ads in Safari when using Youtube, that seems to be the only effective way to block YT ads on iOS.

Without information about your set up it is very difficult to give you any advice. However: You can generally only use one VPN-service at a time on iOS. @protobuff_entropymdescribes a way to get around this by configuring a DNS inside AdGuard’s pseudo-VPN extension.

Maybe of note: IVPN has custom DNS settings in their apps for iOS, macOS, and Windows. Desktops were added this month, but iOS app has had this a long time. I was checking around a few weeks ago and found many VPN providers block using other DNS because of how they implement anti-leak technology. ( I think this is because it’s “easy” to force all DNS traffic to their DNS to prevent your device leaking. And those that do allow custom often only support ipv4 addresses, not DoT or DoH. Mulvad, for example, is a highly rated VPN, but they don’t seem to have custom DNS support.