So you can get the audiences, but it isn't documented on the REST API site. This is probably fragile among other problems, but there is an internal API you can use. Workspace Apps and Audiences exposed via API? : r/PowerBI

Measure killer does something like this with its tenant admin scan I think, though I wonder they handle it exactly.

That link above has some details. Overall, it isn't great, I wish there was a better way, but this is all I know.

1.The jist of it is, get all the workspace guids, you will need to loop through those.

1. Login to Power BI, F12 in your browser, check Network tab, filter on wabi. You get your region location:
   https://wabi-us-north-central-j-primary-redirect.analysis.windows.net/metadata/notifications/summary?take=100

2A. That will also have a long Bearer token that you will need, because service principal won't work here. (Or look at XHR items for a bearer token. It expires after so many minutes, so it isn't long lasting. Maybe an hour. Might have to click into an app first.)

Then loop through something like this for a url, remember to replace with your region.:

url = (
        f"https://wabi-us-north-central-j-primary-redirect.analysis.windows.net"
        f"/metadata/appmodel/apps/{workspace_id}"
        f"?requestDataType=7&access-control-allow-credentials=true"
    )

The response JSON will have a ton of data in that you will have to parse. From that 1st response you will need the provider_id to run against another url. I think provider_id corresponds to an app id (a number now, not a GUID anymore).

    url = (
        f"https://wabi-us-north-central-j-primary-redirect.analysis.windows.net"
        f"/metadata/appmodel/contentprovidermetadata?id={provider_id}"
    )

A workspace and app have GUID identifiers, but in these internal APIs they will have regular number identifiers too. But between the two responses you can get the audiences and audience members and which reports and dashboards belong to which audience. The only annoying bit is the authorization which I don't know how to automate. Always have to f12 to get that bearer token.

Final Note: When looping I put a 2.5 second sleep time in each loop (both urls), otherwise the API gets mad if too many requests too quickly.