I understand this isn’t what you asked but for me in a similar use case I use a wireless keyboard that has a built-in track pad. Sure, it’s not in general as easy to use as a mouse (for me) but if there is no defined key combination or there is but you can’t remember it 
then using the track pad gets the job done. (NB: This is not relating to the Librem 5. I don’t know whether there would be any challenges specific to it.)
2 Likes