Is there a way to use one of these on iOS on mobile data? I've only seen a DNS override option for Wi-Fi.

Install a configuration profile that configures DNS. This a better way to configure DNS on Apple platforms because it's device-wide, not per-network. These are generally distributed as files named something.mobileconfig. I use one distributed by AdGuard for their public DNS. Just open on an Apple platform and it will offer to install. It's signed, so the OS knows it's from who it says it's from. I have this profile installed on my iPhone, Mac and Apple TV.

https://adguard.com/en/blog/encrypted-dns-ios-14.html

Cool, thank you! Do you know if iOS falls back to the local DNS if necessary, e.g. if a visited Wi-Fi blocks a given DoH?

I don't think there's any automatic fallback, but I'm not sure.

It is possible to quickly toggle on-and-off what the configuration profile sets in Settings. I've occasionally had trouble on captive wi-fi portals, like on planes, but I generally remember it's probably the DoH, so I go toggle it off, get connected, and toggle it back on.

Oh, that’s cool, I assumed I’d have to uninstall the profile in that case so I never gave it a try.

Thanks again!

you can also have a look at nextdns [0][1]. I set it up on both my mac nad iOS. NextDns provides a panel where you can see what got blocked and some other analytics for you. Even though I use Brave on iOS and Arc with uBlock Origin still that wasn't enough and nexDNS blocked some additional ~8% trackers. It's free for first 300k requests per month.

[0] https://nextdns.io/

[1] https://github.com/nextdns