Anyone please?

  @mulmj2 

I have the Deco BE16000, and my system is missing this feature also (I probably watched the same Youtube video as you did).  I also purchased my system for the dedicated wireless backhaul.

I'm pretty sure I read something about why the feature is not present - but I don't remember exactly where or the details.  

On my system I can set an SSID for 5 GHz and 2.4 GHz, while also being able to set a different SSID for the 6 GHz network.  My system is quad band with two 6 GHz bands.  I am assuming one of those is for the dedicated wireless backhaul.  Even if this is the case, I set my SSD for the 6 GHz to hidden with a password that no one has.  I would assume on a tri-band system with one 6 GHz band, this would effectively utilize the 6 GHz band as a dedicated backhaul. 

As far as range, my experience is similar to yours.  I have watched a lot of range tests on Youtube and I do belive that TP-Link's claims are correct under ideal situations.  The problem is that each environment is unique between type of construction, obstructions and interferring congestion.  Minor changes in placement can make a big difference.  After moving the Decos around a little and re-running the Optimize network feature, I feel like I have pretty good coverage and range now.

Hopefully someone else more knowledgeable can jump in and give you some more answers.  I just wanted to give you some feedback from my perspective since I also had similar questions when I first got my Deco system going.

  @Mike101 

Given that all wifi channels are always available for the backhaul, I believe the logic of the app has been changed.

In the past, it was possible to setup wifi 6 is "only for backhaul".

Now, it is possible to explicitely activate or deactivate the availability of wifi 6 for regular devices.  Exactly has was done before for wifi 2.4 and wifi 5.

I believe the new approach is easier to understand.

I agree that the change of logic is confusing.