Hi,
With @HIRAM’s help, I can control RT from Python scripts. It seems that the problems are caused by notarization (or sandbox).
However I cannot succeed in controlling a notarized application (RT) from another notarized application (GIMP) through Python scripts.
If you don’t mind, instead of this plug-in please use the plug-in below with ART which is a fork of RT.
ART is not notarized and there aren’t problems like RT. However you should follow the instructions below, when you install ART.