Hey,
why are you not just running the .pkg file?
The .so file is contained in the .pkg file and it will take care of copying everything to the correct place.
In general it might be a good idea to ask questions related to this plugin in the plugin's thread to get help quicker :)
EDIT:
Please also take note that at least OBS 26.1 is required to run the latest versions of the advanced scene switcher plugin.