@Kevin_Z 

Thanks for the reply. 

That's the information I found, however, I cannot for the life of me find an option within the settings to enable the 6Ghz band for wireless backhaul.

I have now set all SSIDs for all three bands to the same name, but I still cannot see the option to enable it within the web management interface.

Before tonight, I had been managing my devices via the iOS app, but after accessing the web management console (which I didn't know existed) I was able to confirm that my iPhone 15PM is connected to the 6Ghz band, as the app doesn't show this:

TP Link technical support advised that a firmware update will enable this along with EasyMesh for the RE815XE. 

  @Kevin_Z 

Thanks for responding.

From my understanding, the devices are connected wirelessly using all three bands. The Router/RE decides which bands to provide a signal, but the sooner TP-Link allows you to configure which band the better.

Even on the back of the box, it seems to indicate the 6Ghz band can be solely used for the wireless backhaul:

  @Kevin_Z 

I see, that makes sense, that the software optimises the devices, but it would be great to have the option. Hopefully, this can be implemented.