By default, renderStacks will not do anything. You need to tell renderStacks what to do. Everything is pmodifier. There is no “default” pmodifier. But, if you want to have a custom start setup for you. You can save startup file using Preferences menu > Save startup file
Set your default pass and pmodifiers(expecually RenderOutput pmodifier). Then run this command.
The startup file will be saved in your User Settings folder.
C:\Users\[username]\Autodesk\3ds Max 2021\User Settings\startup.xml
Every time when renderStacks runs first time for a scene or File menu > Reset. This file will be loaded.
You can use rsStartFilePath environment variables for central control of this startup file.
If you use this env var, renderStacks will not allow you to save the startup file.