@ljCharlie What is your configuration?

Did you directly connect the wired device to a Deco?

Is your Deco network operation in AP or Router mode?
In the list of devices displayed by the Deco app, do you see all wifi and ethernet devices?

  @yves_b 

Here's what I have. The Deco has 4 ports, I think. My Internet line goes into one port, then another port is use to go into my 16-ports switch, one port is used to for my device, and then fourth port goes into another 8-port switch. The second deco is connected via Ethernet to my 16-ports switch. Both deco is using the same SSID even though they are in different part of the house. All of my other devices are connected to the Deco via Wi-Fi.

 

Operation mode is set to Wi-Fi Router. As far as I know WiFi devices and wired devices are able to access the Internet. And yes, in the Deco app, I do see all my devices regardless if it's WiFi or Ethernet connected.

  @ljCharlie 

In the app, if you sort the clients by network type, instead of by connection type, do you see all clients under "main network"?

  @yves_b 

Are you referring to this "Main" network here? I'm not sure where to sort by "Main Network".

  @ljCharlie 

If you look at the first image you shared, on the line with "online clients (41)", on the right, there is a blue icon allowing to change the way the clients are sorted.

I suggest sorting by network type, in order to verify that all clients are on the same "network", the "main network".

  @yves_b 

Yes, I found it. All my devices are there. Here's my iphone and the Marantz AVR.

  @ljCharlie 

Okay, it turned out a bunch of my devices are in isolation mode. That is why my iphone is unable to communicate across different connection type.

  @ljCharlie 

I was wondering about that, and neglected to ask, because it would have been too obvious.
Does that solve the issue?

Yes, that seems to solve the issue. My iPhone can connect to my AppleTV and AVR and other devices now and vice versa.