1.) Open Settings --> Connections --> More connection settings --> Private DNS
2.) Check Private DNS provider hostname
3.) depending on what you want to enter either:
dns-family.adguard.com (To block adult sites)
dot-de.blahdns.com (small hobby project with adblock)
These are secure DNS servers that have integrated ad blocking.
4.) Press Save & enjoy ad-free browsing.
5.) An extra step for Chrome users:
Open Chrome, type in chrome://flags
search for async DNS resolver (#enable-async-dns) and choose disabled in the drop-down menu. Otherwise, chrome could use a built-in DNS resolver which does not block ads.
Last time, at least in my experience adguard DNS has a lot of slowdowns. If you experience a slow internet connection, maybe that's the problem. Also, it's working for Android 10 too.