For anyone running on Android 9 (edit) or later, navigate to
Settings -> WiFi and Internet -> Private DNS
Select Private DNS provider hostname
Add dns.adguard.org (DNS over TLS)
Click save.
Visit https://googleads.g.doubleclick.net/ and you should see browser's 'Server not found' instead of Google's (disable existing ad-blockers or they might jump in and block the URL anyway)
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For anyone on Android 4.0 or later, consider using Google's Intra [0] to use adguard DNS over HTTPS, if you prefer it over cloudflare's or google's.
Install Intra.
Open the app, click on Settings.
Choose customer URL and paste: https://dns.adguard.com/dns-query
Be sure to 'lock the app' to prevent it from being killed in the background.