I remember that VSTi in the Ms Windows had some choice like “enable keyboard” that would focus keyboard on VSTi. Otherwise you were still focused on renoise.
My problem is that with Linux this choice isnt here and some VSTi steal keyboard so i can not change parameters in GUI and play notes on keyboard simulatenously.
If you click anywhere in Renoise and away from the plugin UI, you give focus back to Renoise. If you click the plugin UI, you give focus back to the plugin. In Kubuntu I can use Alt+Tab to switch between the plugin UI and Renoise, and that makes it a bit easier.