Your debug log shows you've configured your Pi-hole to use its own IPv6 address as upstream DNS server:
-rw-r--r-- 1 root root 1.5K Sep 25 11:39 /etc/dnsmasq.d/01-pihole.conf
server=192.168.178.1#53
server=fd00::cd04:26de:3053:2191
interface=eth0
rev-server=192.168.178.0/24,192.168.178.1
server=/fritz.box/192.168.178.1
This can cause a DNS loop.
Remove that IPv6 from Pi-hole's Upstream DNS servers at Settings | DNS.
It also shows that you have enabled Pi-hole's Conditional Forwarding while using your router as Pi-hole's upstream at the same time.
If your router is Pi-hole's only upstream, enabling CF is not necessary in that scenario, as your router would process all forwarded DNS requests anyway.
Furthermore, your router's DHCP server is distributing its own IP as DNS server:
*** [ DIAGNOSING ]: Discovering active DHCP servers (takes 10 seconds)
Scanning all your interfaces for DHCP servers
* Received 548 bytes from eth0:192.168.178.1
Offered IP address: 192.168.178.19
DHCP options:
Message type: DHCPOFFER (2)
router: 192.168.178.1
dns-server: 192.168.178.1
It would be preferable if you would configure your FritzBox to distribute Pi-hole's IPv6 as DNS server instead.
With regards to your FritzBox settings, have a read of our configuration tips at Fritz!Box (EN) - Pi-hole documentation (also available in German).
And finally, it would seem that you've overwritten /etc/dnsmasq.conf
:
*** [ DIAGNOSING ]: contents of /etc
-rw-r--r-- 1 root root 27K Feb 5 2021 /etc/dnsmasq.conf
dhcp-mac=set:client_is_a_pi,B8:27:EB:*:*:*
dhcp-reply-delay=tag:client_is_a_pi,2
As this file normally points to conf-dir=/etc/dnsmasq.d
, absence of which now would prevent pihole-FTL
from reading any of its configuration located in /etc/dnsmasq.d
.
Run
pihole -r
with Repair and verify that /etc/dnsmasq.conf
content has changed.