Content of /etc/systemd/resolved.conf
:
[Resolve]
#DNS=
#FallbackDNS=
#Domains=
#LLMNR=no
#MulticastDNS=no
#DNSSEC=no
#DNSOverTLS=no
#Cache=no-negative
#DNSStubListener=yes
#ReadEtcHosts=yes
Uncomment (remove # from the front of the line) the DNSStubListener= line and also change the DNSStubListener= value from yes to no.
[Resolve]
#DNS=
#FallbackDNS=
#Domains=
#LLMNR=no
#MulticastDNS=no
#DNSSEC=no
#DNSOverTLS=no
#DNSStubListener=yes
DNSStubListener=no
#ReadEtcHosts=yes
Create a symbolic link for /run/systemd/resolve/resolv.conf with /etc/resolv.conf as the destination
sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
sudo systemctl restart systemd-resolved
DNS server used by FritzBox can be set in Internet -> Zugangsdaten -> DNS-Sever Tab.
Enter Pihole Address both for "Bevorzugter" and "Alternativer" Server, and both for IPv4 and IPv6. IPv6 can use local address, e.g. fd00::96de:80ff:fe22:653b