Rather than tuning VNC I suggest using Stellarmate in server mode and running KStars from another PC/Laptop that connects to Stellarmate over the network. Bandwidth requirements are much less onerous, the overall experience is very smooth and you will also save a great deal of CPU and memory resources on the Pi.

I'm currently running KStars either on the Mac Desktop or an Ubuntu laptop without any network issue. Even over WiFi.
Unless you have a very specific use case I suggest to try.

Have a look at:
www.stellarmate.com/help/ConnectingfromEkosviaEthernetWiF.html

Regards,
Giorgio

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