From what I can see there is no way to achieve “Circle view” within MSFS.
Drone mode is close, but in drone mode you can EITHER control the drone OR control the plane (swapped using “C”), never both at once. If they added a toggle to control BOTH the drone AND the plane at the same time, then we could use it like circle view.
The External view is also close, but, as we all know the camera still turns with the plane. This makes it a lot hard to sightsee from outside the plane imo, because I can never have full control over what the camera is looking at while also controlling the plane.
I’m in the same boat as OP here. I mainly used the Circle camera in XP, and I really miss it in MSFS. Even MSFS 2000 and the various MS Combat Flight Sims have a view that works just like circle cam. I’m surprised and disappointed that the views in MSFS 2020 are currently so limited. (that being said, hats off to the dev team. Flying from inside the cockpit without trackir is better than I thought it could ever be with all the snap views and different angles. I’m just bummed that I can’t make my go to external/sightseeing view work in this sim)