Ahhh — I think I got it 🙂
I set the buttons up using the Dynamic Data options in the WordPress sidebar, as opposed to using the Dynamic options that appear directly above a selected element.
^^ aria labels with this dynamic data setup were not working.
I reset all the dynamic options to the ‘old’ way and the aria labels now work perfectly 🙂
Am I not using the sidebar dynamic data options correctly?
You the best 🙂