You seem to be running an older development branch of pihole-FTL:
*** [ DIAGNOSING ]: contents of /var/log
-rw-r--r-- 1 pihole pihole 62427 Jun 6 23:25 /var/log/pihole-FTL.log
-----head of pihole-FTL.log------
[2021-06-06 21:36:33.447 17816M] ########## FTL started! ##########
[2021-06-06 21:36:33.447 17816M] FTL branch: fix/hourly_PTR_requests
[2021-06-06 21:36:33.447 17816M] FTL version: vDev-b833b73
[2021-06-06 21:36:33.447 17816M] FTL commit: b833b73
[2021-06-06 21:36:33.447 17816M] FTL date: 2020-12-01 14:18:44 +0100
If that is not by intention, you should consider reverting back to the master branch.
In addition, your debug log shows someone has altered Pi-hole's web server code:
*** [ DIAGNOSING ]: contents of /var/log/lighttpd
-rw-r--r-- 1 www-data www-data 2932 Jun 6 23:26 /var/log/lighttpd/error.log
-----head of error.log------
2021-06-06 00:00:10: (server.c.1759) logfiles cycled UID = 0 PID = 10691
2021-06-06 07:21:43: (mod_fastcgi.c.421) FastCGI-stderr: PHP Notice: Undefined index: cameras in /var/www/html/index.php on line 83
/var/www/html/index.php does not contain any reference to
cameras, not in line 83 nor anywhere at all.
If you are you running any custom scripts for Pi-hole, you'd probably have to consult their respective maintainers on how to revert those.
As for your observation, your debug log confirms your Pi-hole is not responding to DNS requests arriving through its local IP nor to DHCP broadcasts while
pihole-FTL is reported as active:
*** [ DIAGNOSING ]: Name resolution (IPv4) using a random blocked domain and a known ad-serving domain
[✓] ns2.srix.ru is 0.0.0.0 via localhost (127.0.0.1)
[✗] Failed to resolve ns2.srix.ru via Pi-hole (192.168.0.5)
[✓] doubleclick.com is 220.127.116.11 via a remote, public DNS server (18.104.22.168)
*** [ DIAGNOSING ]: Discovering active DHCP servers (takes 10 seconds)
Scanning all your interfaces for DHCP servers
DHCP packets received on interface lo: 0
DHCP packets received on interface eth0: 0
*** [ DIAGNOSING ]: Pi-hole processes
[✓] lighttpd daemon is active
[✓] pihole-FTL daemon is active
As both DNS and DHCP are affected, this would make a firewall issue likely, yet you already checked that ports are open.
But your debug log also shows:
*** [ DIAGNOSING ]: Operating system
[✓] Distro: Raspbian
[✓] Version: 10
*** [ DIAGNOSING ]: SELinux
[✓] Default SELinux: permissive
[✓] Current SELinux: Disabled
That is an unusual combination.
I wasn't aware SELinux is available on Raspberry Pi OS kernels.
Did you compile your own kernel to get this running?