I installed it this morning, headless on Ubuntu. The command "cloudflared proxy-dns" does work without a cloudflare account. For me on Ubuntu 18 anyway.
I mostly followed these directions:
Connect to 1.1.1.1 using DoH clients · Cloudflare 1.1.1.1 docs
cloudflared (DoH) - Pi-hole documentation
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apt install cloudflared
nano /etc/default/cloudflared
Paste:
CLOUDFLARED_OPTS=--port 5353 --upstream https://1.1.1.1/dns-query --upstream https://1.0.0.1/dns-query --upstream https://[2606:4700:4700::1111]/dns-query --upstream https://[2606:4700:4700::1001]/dns-query
nano /etc/systemd/system/cloudflared.service
Paste:
[Unit]
Description=cloudflared DNS over HTTPS proxy
After=syslog.target network-online.target
[Service]
EnvironmentFile=/etc/default/cloudflared
ExecStart=/usr/local/bin/cloudflared proxy-dns $CLOUDFLARED_OPTS
Restart=on-failure
RestartSec=10
KillMode=process
[Install]
WantedBy=multi-user.target
systemctl enable cloudflared
systemctl start cloudflared
Then in pihole add "127.0.0.1#5353" as your custom DNS server