since Bullseye release is near and actual pre release is running fine already, I decided to test Pi-hole on it.
Except the webinterface everything is working.
It seems that the lighttpd config is not compatible because after Pi-hole installation lighthttpd does not start any longer. I restored default config and lighttpd starts again. I will use Pi-hole without webinterface and maybe I will try to figure out what causes lighttpd to crash with Pi-hole config file.
If someone already has a solution please reply to this post.
greetings from Berlin