@DavidWalsh 

I think I have an idea why you do not see Connection Preference option for this installation, but I need more information from you to be sure. For that new setup, open its Update Deco page in Deco app, make screenshot and share here.

That page will give the summary of Deco units in the setup and their firmware versions.

Example:

  @Alexandre. 
 

  @DavidWalsh 

As I suspected.

For the same Deco model, such as M4, TP-Link produces it with different hardware versions. Then, it provides firmware with different feature sets for different hardware versions.

You have three Deco M4 on firmware 1.6 (Garden, Living, Louis' Rooms), this firmware does not support Connection Preference. If you need connection preference in that setup, you will need to remove (delete) all three and replace them by three Deco M4 that support Connection Preference, which will be firmware 1.1.2. Same as Kitchen, Living, Utility.

If you have multiple M4 setups, find those that do not require Connection Preference, see if they have M4 with firmware 1.1.2 and swap them with those.

Alternatively, as it appears to be a three-set with firmware 1.6, return it to retailer for refund and get different set with different hardware version, the one that runs with firmware 1.1.2.

  @Alexandre. 
 

That's brilliant, thank you! I will have a look later and report back here of the progress. 👍

  @DavidWalsh 

Just a quick question, can the 1.6.2 units have their firmware reverted to 1.1.2?

  @Alexandre. 
 

This is fantastically informative, thanks very much! Plenty of things to go at 👏👏👏