@hedders @unixorn I have this setup and my devices aren't adding ".fritz.box" to the domains. As far as I understand DNS suffixes are just added if I do not fill in a complete domain.
This is something I could reproduce. If I type "http://test" in the browser, the domain request in Pi-hole is listed as "test.fritz.box". If the domain is complete "google.com" nothing is added.
I added a wildcard for "fritz.box" in my Pi-hole and everything is working normally.
Am I missing something?