You configured Pi-hole to listen on ethernet but it seems there is no ethernet connection, but instead a wifi one
*** [ DIAGNOSING ]: Networking
[✗] No IPv4 address(es) found on the eth0 interface.
[✗] No IPv6 address(es) found on the eth0 interface.
*** [ DIAGNOSING ]: Discovering active DHCP servers (takes 10 seconds)
Scanning all your interfaces for DHCP servers
Timeout: 10 seconds
* Received 300 bytes from wlan0:192.168.12.1
Offered IP address: 192.168.12.123
Server IP address: 192.168.12.1
Relay-agent IP address: N/A
BOOTP server: (empty)
BOOTP file: (empty)
DHCP options:
Message type: DHCPOFFER (2)
server-identifier: 192.168.12.1
lease-time: 86400 ( 1d )
renewal-time: 43200 ( 12h )
rebinding-time: 75600 ( 21h )
netmask: 255.255.255.0
broadcast: 192.168.12.255
router: 192.168.12.1
dns-server: 192.168.12.1
domain-name: "lan"
--- end of options ---
DHCP packets received on interface lo: 0
DHCP packets received on interface eth0: 0
DHCP packets received on interface wlan0: 1
PIHOLE_INTERFACE=eth0
Run pihole -r and choose the right interface.