Pi-Hole in Docker in PROXMOX .... but does not work yet?!

Hello,

I have installed Pi-Hole (and some other applications) in Docker (and another LXC container) in PROXMOX. It runs on a jailbroken Chromebox 3.
The Pi-Hole administration at http://192.168.178.30/admin/ works fine.
I have added some adlists and deactivated some of them, so that I currently have about 10 million blocked domains.

Unfortunately, I can't get Pi-Hole to actually block the domains.
In the Fritzbox under -> Home network -> Network -> Network settings -> IPv4 settings. Under "Local DNS server" (default was 192.168.178.1) I have now entered the IP of the Pi-Hole: 192.168.178.30

In the Pi-Hole I have entered under -> Settings -> DNS -> Upstream DNS Servers -> Custom 1 (IPv4) -> 192.168.178.1 (IP address of my Fritzbox).

IPv4 Primary and Secondary Cloudflare (DNSSEC) was set, I deleted it.
I only set IPv4 Secondary OpenDNS.
Advanced DNS settings:
I have deactivated: Never forward non-FQDN A and AAAA queries
I have deactivated: Never forward reverse lookups for private IP ranges

The result is: All websites and also some Pi-Hole test pages are still loaded with advertisements. Apparently nothing is blocked.

Where is the error?

Many thanks and best regards,
Chris

Please don't open multiple topics for the same issue.