@David-TP 
Meanwhile, 2 years have passed and it is still not possible.
I have turned of the mesh tech for my 2 cameras and they still chose to connect to my living room deco, even though they only have 1/5 of the signal strength of the deco being in line of sight of both cameras with full signal strength!

I really like your mesh system, but you need to impove it at a faster pace. It would cost absolutely nothing to you to add this option, you can even add a warning that i may not help or even worsen the connection and leave it up to the users to decide!

2022 and this functionality is still not present. Have to do the hacky workaround of turning mesh off for the device and changing my wifi adapter's roaming aggressiveness, and that still doesn't always prevent my stationary desktop pc (also using a TP-Link wifi card) from disconnecting from my main deco (that gives me full signal strength and 350mbps down) to the one on the opposite side of my house (that gives me less than half signal and 11 mbps down)

I have wireless cameras doing the same thing. They connect to a deco so far away that they are unreachable and completely stop working.  Eventually they connect to the full-speed close deco and work fine but it never sticks.

We desperately need to lock devices on a single deco or perhaps white/blacklist individual MAC addresses per deco.  Something...

  @Mike1234 At this point I've turned off the 3rd router on my 3rd floor since nobody is up there anymore.  This has made it more normal in that it only has 2 to choose from and it does a better job in choosing.  It is ridiculous that an update was promised and not delivered, and I'd say it will NEVER come.

I did a speedtest before I hit post just to see and it appears to be on the main router as it should be.  On a satellite router it would be a 10-20% degradation in speed.  That isn't so much but it impacted internal streaming of music since it bounces around so much in my setup anyway with all the components.

Just found this thread. I have the exact same request - specifically because of my security cameras. The main reason I got mesh was so that my outdoor cameras could connect to the same network as my other devices, and my previous router couldn't produce a strong enough signal to get through 120-year-old brick/stone walls. The Deco works great, until for one reason or another they connect to the main one, which has almost no reach to the outside, rather than the nodes which are right by each camera and provide plenty of signal.

I really hate the Deco.  None of the "disable mesh" options work, and it's become useless for my purpose.  I'm better off with an old-fashioned extender, even if it does require a different network name.  FWIW, I have one of the WiFi 6 tri-band Deco models.

  @R5Ryder I am super frustrated with this exact issue. Can't believe they still don't let you control which devices connect to which node.

  @David-TP 

Hi , it looks like its been some time since this question was asked to fix a device to a single deco. This issue is a big issue and seems like a quick fix could be done. When is this planned in to be added or do I need to look at another company to get this basic option? i understand that a mesh system is self fixing but I am getting devices with wifi signal as low as 10% when I have a mesh device only a few feet away but the mesh system is using that mesh point some 100 ft away.

  @Razr  There is a way to set the preference.  Check out the overview tab.  There is a list of clients.  Choose your client. Hit the settings icon on the top right. Locate connection preference.  The rest is self explanatory. 

Users with cameras should definitely check this feature out.