@Generaltwig An excellent diagram, well thought list of questions. I would love to take a shot at it. I think I can provide you with the right answers and necessary recommendations, but one critical...

@Alexiezt Try these two things together: 1. Switch Deco mesh to Access Point mode: Switching a Deco to Access Point (AP) Mode 2. Configure Main Network to run on 5GHz exclusively: Run speed tests...

@Mrget It is possible, see picture under question Q4 of this FAQ: General questions about Ethernet Backhaul feature on your Deco For this to work for sure, you need to have an option to configure...

@Adex1 The feature to force device on a specific band and to connect to specific Deco is available for newer Deco models with never firmware. It is described in How to select a preferred signal...

@Splatterly If Internet dropped completely for every device connected to Deco mesh at once, the reason may be somewhere else, but disabling WiFi on router is still necessary step in troubleshooting....

@Splatterly Deco mesh runs its own WiFi network, it won't share or extend router WiFi even if they configured with same SSID. Think of Deco mesh as a WiFi router, the one that can cover large...