At this point, you'll have to manually provide a DNS provider, which the CloudFlare app does for you automatically. ZDNet suggested several, such as "dns.google," which should work. Congrats!

Known as 1.1.1.1, the app, available for both Android and iOS, works by changing a user’s Domain Name System (DNS) address. “DNS is the Internet’s directory,” Cloudflare writes. “Click ...

Enter the above in the Private DNS provider hostname section and then tap Save. You’re done. You can exit out of Settings and enjoy your new Private DNS over TLS feature in Android Pie. The Caveat ...

In some phones, private DNS is automatically configured. However, if not pre-configured, desktop and phone users have to enter the IP address of a private DNS server.