new install of 64bit Xubuntu (18.04.3): Installed by adding the repo.
(I do have an nvidia card if that matters, but not using the prop driver.)
markp@markp-ThinkCentre-M91p:~$ insync start --no-daemon qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found. This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem. Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, webgl, xcb. Aborted (core dumped)