I am not sure why, but the only ad campaigns I see are those created inside HighLevel?

External campaigns (Created outside of HighLevel) need to show within HighLevel.

To start with, even read-only is fine. (Longer-term, could also add edit these campaigns).

It should not be difficult to import these campaigns as read-only in the meantime.

Yes, the reporting/Google Ads, does give reporting. However, the ad manager is totally blank - unless campaigns are created inside it