@SrDarkWarrior Mine doesn't appear to, at least not by following the directions to access it

There is no web server running on the LAN gateway address under any of the standard ports

@BluePic 

Just http to the IP address it shows on your phone ap, enter the username and password you entered when you set them up and you should be in.

Have to warn you: be prepared to be seriosusly underwhelmed - you still need the phone app to manage.  This is still a long way from being a mature, fully functioned, product.

@SmilingEddie 

Nope, there is nothing running on either port 80 or 443 at the gateway address

@dougis 

Might have found your problem, faced with it myself.

I'm using them in Access Point mode. It means that you can't assign a fixed IP address to any of the units, its assigned almost randomly from the pool you defined in your DHCP config.  I've lost connection with the web page and have found that it has assigned a completely different address from the pool from last night.

As you know, DHCP normally renews the lease if the the address is still active. For some strange reason, Cisco DHCP treats the Deco units different from all other devices on the LAN in this respect

Why didn't TP-link developers see this one coming when they imposed DHCP on the Deco 9 Plus in Access Point mode? 

Does Deco M9 Plus support web-based management? Not in Access Point mode unless you're prepared to go to the phone app and see what address is currently allocated to the main device and then open your web browser.

Leaving them in router mode lets you assign an IP addreess but is even more problematic: introducing a second DHCP source for a start.

@SmilingEddie 
Nope, I am in router mode with a fixed gateway IP, nothing is responding on that Ip over the standard ports (just times out)
The only ports a scanner shows open are 22 and 53 and I am not SSHing in for a command line :-)

@SrDarkWarrior where do we get the firmware with the web ui? Still no updates are available, according to the Android app. Still on 1.2.12 build20191014 rel 42025.

Thanks!

@BluePic 

The automatic firmware update that kicked off when I connected then to my LAN has it.

It was then just a matter of HTTPing to the IP address.

As stated previously,this is not a web-based management console; it just gives you very basic information and no ability to change settings.