@anon55913113 I see what lead to the misunderstanding. Yes, it is the Fritzbox that requests the no-caching by not providing a TTL at all.
My assumption would be that it may be requests ending in fritz.box go to the Fritzbox (which replies with: I don't know hat you want) and others manage go out (because conditional forwarding isn't triggered for them)? Looking at your screenshot above:
they seem to result in N/A meaning the upstream never replied with any answer. Silence is of course different than NXDOMAIN.
No. 1 still doesn't make much sense as, when I directly query the Fritzbox, I do seen this issue. However, I guess with Conditional Forwarding you won't see a difference between 1 and the solution including CF ?
Unfortunately, this happens more often. I have tried the FritzLabor version and the phones are now able to show a weather screen. This worked for the first day, since then they display "Der Server ist nicht erreichbar." Nothing is blocked in Pi-hole and I don't see why this is happening. I wrote them feedback and on the second try I received quite a soggy reply like: "Fakt ist Ihre 7590 funktioniert einwandfrei. Mehr gibt es da nicht zu sagen." sigh...
You may want to reconsider this. Check out Will DoH & Pi-Hole Still Work With A Recursive DNS Server Setup - #4 by yubiuser