@OliJ 

Hi,

Have you already verified that the light bulb is actually able to connect to the Archer AX53's 2.4 GHz network if Smart Connect is disabled?

In case it is able to connect while Smart Connect is off, will it stay connected when you re-enable Smart Connect again?

  @OliJ 

I didn't mean to suggest separating the networks permanently. I merely suggested to test if the light bulb will connect to the Archer AX53 at all, because there could be a reason other than Smart Connect for the light bulb not connecting.

So, pick a time when no other people are using your Wi-Fi network, disable Smart Connect, then test if the light bulb will connect or not, and then enable Smart Connect again. After that everything will work just like before, nothing will have to be re-configured.
 

  @OliJ 

If you'd like you could read this article here https://community.tp-link.com/en/home/stories/detail/501928 that illustrates the general idea of an IoT network.

However, the way it is implemented in TP-Link's home routers, the "IoT network" is basically just another SSID with different security settings and password, using the same Wi-Fi radio as the main network.

As mentioned in the TP-Link article I linked to above, a second wireless network like the "IoT network" can be very useful if the main network is configured with WPA3 or WPA2/WPA3 Transitional security, but there are one or more older device(s) that can't cope with this new security standard or the mixed mode and require standard WPA2-AES or WPA-TKIP.