It looks like the majority of your DNS queries are coming from the Fritz Box IP, but they are unlikely to be originating with that device.
I do note that your DHCP server (the Fritz Box) appears to be passing out it's own IP for DNS, and not the IP of the Pi-hole:
*** [ DIAGNOSING ]: Discovering active DHCP servers (takes 10 seconds)
Scanning all your interfaces for DHCP servers
Timeout: 10 seconds
* Received 548 bytes from eth0:192.168.88.1
Offered IP address: 192.168.88.145
Server IP address: 192.168.88.1
Relay-agent IP address: N/A
BOOTP server: (empty)
BOOTP file: (empty)
DHCP options:
Message type: DHCPOFFER (2)
server-identifier: 192.168.88.1
lease-time: 864000 ( 10d )
renewal-time: 432000 ( 5d )
rebinding-time: 756000 ( 8d 18h )
netmask: 255.255.255.0
router: 192.168.88.1
dns-server: 192.168.88.1
domain-name: "fritz.box"
broadcast: 192.168.88.255
ntp-server: 192.168.88.1
Port Control Protocol (PCP) server: 192.168.88.1
DHCP packets received on interface lo: 0
DHCP packets received on interface eth0: 1