You can visualize the "EP Ops adapter..." objects and see "Number of objects collected", which will tell you how many EPO agent objects you're ingesting. What it doesn't tell you is how many unique agents makeup those objects, since that total # objects will be agent objects, os objects, service objects, etc. What is notable is that all Windows and Linux objects have a unique identifier that associates each object to an EPO Adapter Instance (a node). However, there are no properties, metrics, or relationships that represent what you're looking for. I believe you'd actually need to do an API call to pull the resource and their identifiers, then create a table that totals up the # OS that report to each EPO Adapter Instance. Ideally you'd also do a translation of the EPO Adapter instance ID to the friendly collector node name.
If you find this or any other answer useful please mark the answer as correct or helpful.