I know "access denied" can often be misleading and hide other kinds of issues with accessing the file, such as being blocked by AV software. Still, I'd check the file permissions and make sure there isn't some obvious problem there, especially if your normal user account is not a local admin.
I don't recall what error message comes up when RealFlight has problems accessing the Documents\RealFlight Evolution folder, but that's something else that's coming to mind for me since that PF86 folder isn't on drive C:. RealFlight has an arbitrary limitation on the path length for files (less than Windows' 256-character limit), so if the path to ...\Documents\RealFlight Evolution is excessively long, strange things happen. Such a situation would be when you're letting OneDrive "backup" your Documents folder, because that makes the path to Documents much longer because of the long folder names OneDrive uses to organize the local copy of files. Ideally the path to Documents is fairly short and not being redirected out to OneDrive.