If a button has some form of link, you can set an aria label.
If a button does not have a link but has an interaction that opens a pop-up on click you cannot set an aria label (as it can only be set when you define a link).
Agreed but it is inconsistent to sometimes have an accessibility field and sometimes to have to manually enter an attribute. I wish Bricks would have a separate tab for accessibility next to Content and Style with all the necessary attributes in.