Hello,
I used to run Debian 9.x with Kernel 5.1.x with GNOME desktop and Dropbox GUI installed from the Dropbox website (deb file). Usually in the bottom left corner there was a little box to find the Dropbox icon, and to configure it.
After Buster update I still can start Dropbox and see it in "Processes" doing its work, but the GUI cannot be accessed anymore. I did reinstall the lastest Dropbox deb file and made a reboot, same issue. Dropbox has gone invisible ..