alphabetical list of classes http://pro.arcgis.com/en/pro-app/arcpy/classes/alphabetical-list-of-arcpy-classes.htm
alphabetical list of classes http://pro.arcgis.com/en/pro-app/arcpy/functions/alphabetical-list-of-arcpy-functions.htm
there is stuff in the 'Describe' section, maybe AGOL and portal.
maybe some keyword might twig you needs.
Beyond that, if there is a tool in arctoolbox that you use, then the tool can be accessed through arcpy. Every tool has a code example and syntax at the bottom of their help topic
I have used this in the past: ListMapServices—Help | ArcGIS Desktop but it has been deprecated and you should now be using this: Scripting with ArcGIS REST API—ArcGIS Server Administration (Windows) | ArcGIS Enterprise . There are many samples available which you can adapt to your specific needs.