I'm running Pi-hole in a docker container behind a local Ngnx proxy manager, which in turn, is behind Cloudflare. I have assigned a FQDN to pi-hole.
I would like to be able to admin my pi-hole installation from remote locations. However, when I try to access it from the Internet, I get a blocked page from pi-hole. It works perfectly fine from the local LAN with the same FQDN. The block page indicates that the domain was manually blacklisted by wildcard. However, I can't find that black list and have even tried to whitelist it.
For secure access to your private network via public internet connections, you'd have to make use of a VPN, i.e. configure a VPN server in your Pi-hole's private network and configure your aspiring remote machine as a corresponding VPN client.
You could refer to the Guides > VPN section of Pi-hole's documentation for a few configuration suggestions.