@Sunshine I have tried both, setting up as main and well as satellite.

At first, I set it up as the main router. In the wifi settings, I saw a setting for a 6Ghz network. There, I chose "Use 6 Ghz for dedicated back haul"  - the other option was "Use 6 Ghz for Wi-Fi network and backhaul". With this dedicated backhaul option, the 6 Ghz network should not have been available to any device. Still my phone connected using Wifi 6 (it showed 6 on the the wifi symbol on the top bar). My first issue is that - THE PHONE SHOULD NOT HAVE CONNECTED WITH WIFI6. Or is my understanding incorrect?

Once connected to wifi 6, it does not move to regular wifi, even when I move away from the main router and much closer to the satellite routers which were all M9 plus. Even when the signal become so weak that the phone moves to the phone's mobile internet, it does not connect to a nearby M9 plus, it stays connected to the main XE75 and sometimes said - waiting for network connection to improve.

The behaviour is the same even when I set it up as the satellite router. Once latched to wifi 6, it does not let go automatically. I need to turn off and on the wifi setting on the phone.

Please help.