I use vanadium and adblocking on VPN , DNS adblock works as well. Bromite is a good option as well. The thing about putting Firefox on android for privacy/security reasons have a big issue , webview is chromium based . So basically you just get Firefox on top of everything webview has.

AndOTP Foss and all things I want (encrypted backups,qr etc)

Same as every other times when science have disproven religions fairytales. They adapt. God also made those lifeforms

Signal yes, WhatsApp yes but not the meta data, telegram only if explicitly set to encrypted otherwise no.