Use airport express as an Airplay device only

I have an Airport extreme as my main and only WiFi router.
I do not want to extend the coverage of the Airport Extreme. It works fine as is.

I have an extra Airport Express that I would like to use as an Airplay device from my iPhone (which is on the main Airport Extreme WiFi network), without using the Airport Express to extend the existing WiFi network.

Is that possible?

I have the latest Firmware installed on my Extreme and Express devices.

There is an old question similar to mine but its answer is no longer valid.

(see how to use my airport express just to stream music, no interent )

The reason why I don't want to extend the Extreme's WiFi network with the Express, is because when I walk through the house my iPhone switches to the closest WiFi transmitter, and that transition is far from smooth, and I lose connection to most of my Homekit devices and the Airplay audio skips.