One of the things I've always liked in Outlook for Desktop, is that you can easily duplicate an event or meeting by simply dragging it to a new place in the calendar while holding the Ctrl (or Cmd?) button.
This page (https://supertekboy.com/2019/09/03/duplicating-meetings-and-appointments/) contains a short animation that shows how this works in Outlook.
It would be a simple but great addition to have this function in Thunderbird as well!