I'm not entirely sure I understand the DNS issue, but since this new firmware allows you to set the LAN IP range, you should ve able to avoid any conflicts with the WAN IP range. My Pihole RPi is in...

The new firmware that adds a LAN IP setting is now available, at least for me in NL. Installed it and no problems so far. Some interesting other new features too.

There was another power disruption at my home this morning, and my Decos were rebooted. I noticed that the LAN IP did change again, but with an M5 as the main unit, I was able to change the setting...

It's not that you won't be able to set the DNS sever (you can), but whenever the Deco M4 is rebooted, the LAN IP range may change. I've seen it jump to 192.168.0.x, 192.168.3.x and other ranges....

Just because of this issue, I bought a single M5 unit this weekend, to replace my main M4. I can now finally set the LAN IP range. This is a setting that literally every router I've ever used...