Hi Sam
Thank you so much for the advice above. The following comment "In the example I have provided, I've also hidden the "selected" button from the base and added a duplicate of the button to the open layer with the "selected" state showing. This ensures that when the layer is opened, it will read the "expanded" state of the button."
I know how to remove something from the focus order, but feel like I am missing something around how we get alt text on states to appear and hide in the focus order. My alt text that I place on the selected state does not seem to automatically appear in the focus order even though I am ticking the box "Object is visible to accessibility tools."