I responded to someone in comments on a post that may not get as much visibility, and wanted to share something that might help some others who are newer to this.

I referenced Quad9 DNS as probably one of the best private DNS you can use, Swiss based, no log, no tracking, no data to sell, etc. They also implement DNSSEC, DoH, DoT, QUIC, ECS (which you may or may bot want), malware blocking, content filtering, and maybe something else I'm forgetting.

Many DNS sinkhole apps, OSes, or systems can actually utilize Quad9 for your resolver while those systems also block ads. Below is my functional list of systems that I'm aware of, though I haven't tested everything. I believe all are considered FOSS, too. If you don't have a spare Raspberry Pi laying around, try running in HomeAssistant, Yunohost, ZimaOS (previously CasaOS), or others.

DNS sinkhole (Adblocking) apps:

1. Pihole
2. eBlocker
3. Technitium
4. AdGuard
5. uBlock Origin

Feel free to comment and add your own I'm maybe not aware of. I'm no software engineer, but I can read through some code, though not an expert, nor have combed through these personally. Usually I've tested/run at the recommendation of others over the years before my ban on Reddit (for shitting on AI).

Hope this helps!!

Regarding your original comment, since it regards DNS censorship, pointing people to Quad9 does not solve anything, as it is not more immune to censorship than others. You want a DNS resolver that cannot be censored as an upstream to Pi-hole and co? Set up unbound

1. AdGuard

Adguard's dnsproxy also works well on its own. And it can very well spare you much of the overhead. Just pick a few dns providers you trust, query them in parallel and add whatever ad-blocking list you want to use locally. All with such on not that complicated command...

Example:
dnsproxy --listen=127.0.0.1 --port=53 --bootstrap=9.9.9.9 \

--hosts-file-enabled --hosts-files=/etc/dnsproxy/blocklist \

--upstream=https://unfiltered.joindns4.eu/dns-query --http3 \

--upstream tls://dot.libredns.gr \

--upstream tls://dns3.digitalcourage.de \

--upstream tls://dns.digitale-gesellschaft.ch \

--upstream tls://anycast.uncensoreddns.org \

--upstream=quic://dns10.quad9.net \

--upstream=h3://cloudflare-dns.com/dns-query \

--upstream-mode=parallel \

--cache

Yes, that's an unreasonable amount of dns' queried but I just wanted to get a few useful ones listed, also a wide spread from https (http2 and 3), tls and quic.

I never understood the point in setting up unbound and pi-hole. Unbound is perfectly able to use all the filter lists you use with pi-hole, so at this point it's nothing but an additional layer for some fancy webui with stats you never actually look at.

Unbound is crazy easy to setup too!

For private DNS on my phone I've been using dns.adguard.com for a no-install-required adblocker I can set up on anyone's device. Quad9's one (dns.quad9.net) doesn't seem to have adblocking.

Correct, no ad blocking, but it's fully private, no DNS leaks, you can use the malware filtering option too.

Is this the correct URL? https://adguard-dns.io/

Quad9 is a nonprofit based out of Switzerland, they're DNS-focused, not so focused, that's why they don't do ad-blocking. I watched another commenters link to the CTO talking about what the focus is, how they work, etc. He jokes they don't know their customers, because they hold no data at all.

Adguard is a for-profit company that sells services, they're based out of Cyprus, and have varying privacy policies depending on what service out website you're using. Aka, it sounds like they're monetizing your data in some way, shape, or form.
"We store your Personal Data in our own data center located in Frankfurt, Germany. Your Personal Data may be processed by our employees, who can only access your data through their job duties on a need-to-know basis. If you have questions or would like to know from which countries your Personal Data may be accessed, you can write to us at privacy@adguard.com."
If you're OK with that, that's fine, to each their own. They don't sound like a bad company either, don't get me wrong. Everyone will have different needs and wants, and views risks or threats differently.

Is this the correct URL? https://adguard-dns.io/

I don't know, I don't have any accounts with them or anything, I just point the private DNS on my phone to dns.adguard.com. I used Mulvad's one before but it seemed a little flaky, so I can't really recommend that to non-techies (who otherwise would be using nothing).

I'm always keen to try out a more privacy-respecting service (that's why I tried out Quad9, I appreciate your post!) but ultimately ads are privacy-invading malware so that's something I need to block.

Oh I agree ads are a big no-no!

My mobile setup is Proton VPN, "Secure core" (seems like VPN server relay), custom DNS to Quad9, split tunnel only to my XMPP server for improved performance.

Firefox alt browser with PrivacyBadger (from EFF) and a couple other extensions and blockers. Invidious for any YT videos, Materialious for the YT Invidious app.

I think you want to use dmarc, dkim and spf in your open source server application.

Why would I care about dmarc or dkim when those are used for email hosting services?

You said ad blocking for a dns server that is what you want to use

I've never heard of those being used for ad blocking, and not sure how they relate.

DMARC (Domain-based Message Authentication, Reporting, and Conformance) and DKIM (Domain Key Identified Mail) are for authenticating emails and prevents spam or email impersonation. Same with SPF.