Hmm. OK, I've been using AdAway (not AdGuard) as DNS and/or VPN, experimenting with both) under Pixel 9 stock OS, and it mostly works... but some apps and websites still get ads through.

LineageOS w/Adaway root /etc/hosts blocklists was 100% perfect on my older phone... that's my main quibble with trying LineageOS vs. GrapheneOS.

I know some people recommend against rooting, but I've never had security issues doing it and it seemed to offer more bulletproof ad-blocking.