Figured it out. I need to update the variable used in the ngFor and angular change detection does the rest... very nice!
I found that if I double (or perhaps triple)click on the the select element then the option list pops up.
I've a method defined in screen1, i.e., in Code> Functions, can I use this in other screens? How do I call it?
How do I check which platform the code is executing on , i.e., web browers, vs Android APK, vs iPhone?
I want to be able to use this in my Typescript or in an element property, i.e., [[hidden]