But the AXT-1800 isn’t the main router, that’s a Fritz!Box behind the WAN interface. The AXT-1800 only provides the AdguardHome DNS service via port 3053 which is by default not open to the WAN side, where others LAN devices are connected. And it worked with 4.0.3, but it doesn’t with the new firmware.
That’s my config with firmware 4.0.3 which is working: