Android Settings app, Connections, More Connection Settings, Private DNS. It may vary based on your Android version and phone manufacturer. Currently, Android supports DoH only for dns.google and cloudflare-dns.com. All other servers will use DoT onl...
Android already supports DNS over TLS and HTTPS. Set your preferred server in Android’s settings, and Firefox will use that server. 1.1.1.1/help tells me I am using DoH.
