I’ve seen that use_pin property exists in API, but I have no idea how to access to this value, and if it’s possible to know its status for external addons installed: https://docs.blender.org/api/current/bpy.types.Panel.html?highlight=use_pin#bpy.types.Panel.use_pin
Here the help popup shows me a python snippet truncated (and not copyable by using Copy Data Path), and it looks like relative to user screens name, which is probably not convenient.