Raspbian is a totally different animal. The RPF dropped any kind of standards support with regards to networking. SystemD is not all that bad an init daemon, but nothing you read will apply to Raspbian networking. They pretty much decided to do their own thing. If you look at /etc/network/interfaces there is even a 'factory' added notice that the file is for use with dhcpcd only and static addressing will not be used in that file. /etc/dhcpcd.conf (note the spelling, it's got an extra d in there), is the file for static addressing. Hence that's where we drop our configuration.
To get you back to where you were before Pi-hole, edit that file and remove the information we added to the end: Pi-hole static IP address installation function. Once you're back on the network we can work on a way to get the Pi-hole back on and working with your specific setup.