At least your GPU is regonised by X-plane. X-plane runs better with NVidia than Radeon, but that wouldn't explain such a bad frame rate.
I would start by deleting (or renaming or moving somewhere else as a backup) your "X-Plane 11\Output\preferences" folder. Many bugs have been mysteriously fixed this way.
Then I would follow the settings recommended in that very good video by Q8pilot:
Many bugs can also be fixed thanks to this page, but this is more for reference :
To finish with, I would recommend updating to the latest beta (check the relevant box during the update process thanks to the downloadable X-plane updater, I just hope you can access beta versions in demo mode).
It should soon be 11.02b2.
Let us know what you come up with.