This looks perfect, so I’d guess everything is alright with your box flashing process.
So let’s get back to the DNS which I assume is (still) your problem:
How do you make sure that your Toniebox is aware of your DNS changes? This is kind of a blackbox as you can’t really see what’s happening on the Toniebox itself. So the most important thing is that your DHCP server in the Fritzbox is configured to set your Adguard/Pihole DNS to all clients automatically (including your Toniebox). This is how it looks in my case (*.10 is my Pihole):
Be aware that changing this value might take a little time until it reaches the clients in your network. The DHCP lease for the client (especially the Toniebox) has to be renewed. Don’t know how to force this for the Toniebox. Might need some patience.
Now that you switched to Adguard and followed @inonoob instructions, you first have to make sure that your Toniebox always gets the same ip address from your DHCP server. Activate this checkbox:
Finally you have to set up this rule in Adguard home, replacing [TEDDYCLOUD-IP] and [TONIEBOX-IP] with your ip addresses:
||prod.de.tbs.toys^$dnsrewrite=NOERROR;A;[TEDDYCLOUD-IP],client=[TONIEBOX-IP]
||rtnl.bxcl.de^$dnsrewrite=NOERROR;A;[TEDDYCLOUD-IP],client=[TONIEBOX-IP]
As an example, this is how it would look like in my case, where Teddybox is using 192.168.178.11 and the Toniebox has the static ip address 192.168.178.191:
||prod.de.tbs.toys^$dnsrewrite=NOERROR;A;192.168.178.11,client=192.168.178.191
||rtnl.bxcl.de^$dnsrewrite=NOERROR;A;192.168.178.11,client=192.168.178.191