Update an App Designer listbox if a Simulink model entity is selected

[ Seeking help specifically for this in Matlab 2019b ]

I made an App Designer app that populates a listbox with all the currently open Simulink models. My use-case is:

If a user clicks on one of the open models (or an entity in it like a block or signal), I'd like the listbox Value to switch to the selected model. I'm guessing I'd have to create a listener function.

Below, the first image is the model window and the second is the listbox from my Appdesigner app.

So, if the user selects the signal in the first image (blue) from the BCM_LIB model, I'd like the listbox selection (2nd image) to change to BCM_LIB. Similarly, if this user selected something in the SCCM_LIB window, I'd like the listbox selection to change to SCCM_LIB.

TIA

Joe