I don't know if there is a better way to ask this. But, I mean to open the small down arrow which shows the list of tabs (see following) using a keyboard shortcut <img src="https://i.stack.imgur.com/hfzgy.png" alt="list of files currently opened">

The Command that you are looking for is <code>Window.ShowEzMDIFileList</code>, it can be accessed(at least on my machine) by <kbd>Ctrl</kbd> + <kbd>Alt</kbd> + <kbd>Down Arrow</kbd> <img src="https://i.stack.imgur.com/S6Djh.png" alt="enter image description here">