Screen was flickering outside / in sun with last update. Ran the latest update available and seems to have fixed issue. Spent about 20 min outside and phone adaptive brightness auto adjusted correctly - no flickering and blacked out Screen. I didn't wait for the prompt, went to settings and ran the update
Yup, today's update seems to have fixed this issue on my S20 FE. It started with the previous update but I just tested it out after today's update and it appears to be gone.