In order to execute the script automatically when Agisoft Metashape Professional instance is run you need to place Python script to the following folder:


on Windows: 

   C:/Users/<username>/AppData/Local/Agisoft/Metashape Pro/scripts/


on Linux: 

   /home/<username>/.local/share/Agisoft/Metashape Pro/scripts/


on Mac OS X: 

   /Users/<username>/Library/Application Support/Agisoft/Metashape Pro/scripts/


on any OS (for all users):

   <installation folder>/scripts/


Usually such autorun scripts are useful for adding custom menu options to call the custom processing operations directly from the application GUI instead of using Run Script dialog each time.