You can force a rescan of the community folder in-sim… but you’re not going to like it.
ESC to exit the flight, then go to Main Menu|Profile|Content Manager. Delete one of the Official content. (I use a repaint type I never use). Then outside the sim, use Windows Explorer to add or delete to your Community folder. Go back to the Main Menu|World Map, and start a flight… The folders are rescanned.
(Remember to add back the deleted Official Content you deleted… it will have to re-download and take several minutes).
It would actually be easier to exit the sim, add or subtract from Community, and restart the sim!
I agree that this is bad. A button in the MSFS toolbar to rescan/refresh the scenery would be better. Also the Content Manager needs to be able to delete/add/inactivate Community packages.