Well, these are indeed solid workarounds. The first one is kinda for me... BUT - If one connects pihole device to the "outter" router, and the wi-fi clients are connecting to Deco, you will not see...

I'm also thinking about changing to some other mesh devices, since I can't use the guest network without those settings available, and because @TP-Link didn't even care about this since my last post,...

Aaaand here I am with my Deco M4 and pihole that doesn't work on guest network... Please, TP-Link, add the guest network DNS option. You've added so much useful stuff with updates, that are much more...