The solution below fixed the problem for the user.
The problem is that basically the combination of Shift+Tab
is not unique and may be mistaken when transmitted to the server.
This problem may occur when using VNC between non-Linux and Linux computers.
This same problem is evoked in the post
using Alt-Gr from a Windows VNC client to vino.
Although dating ...
If the reason why you need this is because of bandwith limitations (e.g. low connection speed), then, as Darth Android said in a comment, VNC already transmits only portions of the screen that change.
In particular, VNC uses the RFB protocol (Remote FrameBuffer) (see this), which is based on incremental updates of pixels, and the official RFC for the ...