You have other services running on ports used by Pi-hole, and this is the cause of your problems. Port 53 is needed by pihole-FTL and port 80 is used by lighttpd. If you weren't running connmand prior to Bullseye, something in your upgrade process installed it. I would visit the forums for your OS and find out how to disable this.
*** [ DIAGNOSING ]: Ports in use
[53] is in use by connmand (https://docs.pi-hole.net/main/prerequisites/#ports)
[80] is in use by apache2 (https://docs.pi-hole.net/main/prerequisites/#ports)
*:443 apache2 (IPv6)
*** [ DIAGNOSING ]: Pi-hole diagnosis messages
id timestamp type message blob1 blob2 blob3 blob4 blob5
---- ------------------- -------------------- --------------------------------------------------------------------- -------------------- -------------------- -------------------- -------------------- --------------------
1 2021-09-13 20:32:41 DNSMASQ_CONFIG failed to create listening socket for port 53: Address already in use
I don't think this is a bug. We support a wide variety of OS's, and any number of other processes can be running that interfere with Pi-hole.
I will note that I am running several instances of Raspbian Bullseye and have not encountered any conflicts on port 53.