I needed to reinstall PiHole (Upgrade from Buster to Bullseye). I always had my own Let's Encrypt Certificate on my own domain to access pihole via https://pihole.mydomain.com. SSL is enabled via external.conf but lighttpd is not listening on SSL:
if you have any modifications for lighttpd via an external.conf file, this file now needs to be mapped into /etc/lighttpd/conf-enabled/whateverfile.conf instead
After creating 99-ssl-custom.conf in /etc/lighttpd/conf-enabled it worked:
root@pihole-master:/etc/lighttpd # ll conf-enabled/
total 4
lrwxrwxrwx 1 root root 32 Mar 5 13:03 05-setenv.conf -> ../conf-available/05-setenv.conf
lrwxrwxrwx 1 root root 35 Mar 5 13:03 10-accesslog.conf -> ../conf-available/10-accesslog.conf
lrwxrwxrwx 1 root root 33 Mar 5 13:03 10-fastcgi.conf -> ../conf-available/10-fastcgi.conf
lrwxrwxrwx 1 root root 38 Mar 5 13:03 15-pihole-admin.conf -> ../conf-available/15-pihole-admin.conf
-rw-r--r-- 1 root root 512 Mar 5 18:37 99-ssl-custom.conf
lrwxrwxrwx 1 root root 38 Mar 5 13:02 99-unconfigured.conf -> ../conf-available/99-unconfigured.conf