during running pihole -up i got the error about an uspported os.
i tried, following the suggestion, the ignore-os option.
Expected Behaviour:
The update ends succesfully.
Actual Behaviour:
The update ends without error.
The admin console (dashboard), shows only the left hand side with the navigation. the right hand side is empty, also the verisons at the bottom are missing.
On the left i can read, that dns is not running. That is right, no name is currently resolved in my network. (For quick help i changed dhcp dns server back to fritzbox).
Locally dns on the raspberry pi was not working because in /etc/dhcpcd.conf static domain_name_servers was configured to localhost, i changed it to fritzbox ip.
As you said: Rapbian 9 is unsupported, so the expected behavior can't be a successful update. Even if you update, the internal dns engine won't start on that OS.
The right solution is to get an up-to-date OS.