Most dynamic changes to a UI component (at least, changes that happen while a user is interacting with it) are communicated through state changes rather than property changes…
It might therefore seem reasonable to also expect a screen reader to pick up and announce state changes but not property changes. However, as with many things related to ARIA, it is not that simple.
Sarah goes into detail about how to properly convey state changes to screen readers and other assistive technology.
This article was incredibly helpful on a project I was working on a few weeks ago. I highly recommend you go read the whole thing.