Hi Jane,
I am having the same issue. It used to work fine, but a few weeks, maybe a few months ago either left or right clicking the icon in the tray does nothing. I reinstalled and updated with no luck.
The CRTL click trick works fine and is a work around, but not the way it is supposed to be. Been using Dropbox for years with no problem and works fine on my Windows 10 laptop on the same account. A screen shot won't help as there is nothing there to screen shot, which is what the issue is. The icon works fine as far as synch indicator.