It is very difficult to star messages using touch because the event seems to be passed onto the scrollbar.
With a long list of messages, trying to star a message in the middle of the display by touching the empty star icon the touch event is passed onto the scroll bar causing cursor to scroll into the middle of the list AND for the star icon to be filled in the message that has been scrolled off the screen. There seems to be too little separation between the scrollbar touch and the star icon.
Another problem that has surfaced is that it is possible to select all messages and to add a star but it is not possible to unstar all selected message unless all messages are first starred.
This problem has been observed on a Samsung Phone (Android 9) and Samsung Tablet (Android 10) with S-Pen.