@gatorback 

Deco's default to 'Smart Connect' it seems. So by default, you have only 2 SSID's, the Guest and the LAN itself. The Deco determines by 'talking' to the device, which BAND to give it, one of 2 or 3 if you have a Wifi 6/7 Deco system.

To individually have both a 2.4 and 5Ghz (or 6Ghz) SSID, you must disable SMART CONNECT.

Different Routers/Deco's have different ways to do this... and on my Deco I have to use the Deco app, not the browser GUI to do this. No direct setting for this like 'smart connect' like on my other older router though. Seems I need to look at the 2.4/5Ghz setting and select only 1, but I am not even sure I could create another one for 5Ghz?

It might depend on the Deco model?

  @IrvSp If it makes any difference, the Deco M4s are configured as Access Points: an Asus router performs DHCP and other router funcitons.

  @gatorback 

The M4 is a dual band unit... but usually the main SSID is defaulted to SMART CONNECT. That combines the 2.4Ghz and 5Ghz SSID as one single one, and the Deco queries the device to decide which band to connect to it.

So you see a SINGLE SSID. Guest Network too.

But look at this document, --> https://www.tp-link.com/us/support/faq/1591/ andon # 4. Tap Advanced->Band to select the operating Wi-Fi band of the Deco.you'll drr how to break the combined band and crate 2 SSID's, on for 2.4Ghz and the other for the 5Ghz band.