I suggest you start with this blog. Creating scripts for Power Shell isn't really a Power BI skillset, but an admin skillset. A good admin can run powershell scripts on any part of the organization, not just Power BI.
There is not one command to do this, but the Power BI REST API can handle this. For example - Admin - Dataflows GetDataflowsAsAdmin - REST API (Power BI Power BI REST APIs) | Microsoft Learn will get a list of all dataflows in the org. There are capacity commands, datasets, workspaces, etc. You'd just need to spend a bit of time in PowerShell writing a script to crawl through the workspaces you want (assigned to those capacities) and export the data in JSON format. From there, just use Power Query to extract that data and write a report in Power BI.
There is also, of course, the Power BI metrics app you have access to, but it is somewhat limited in what it provides, mostly performance related. Super useful, but won't answer your specific question.
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DAX is for Analysis. Power Query is for Data Modeling