Cannot access to other folders by RNFS.exists()

I use react-native-webview in my react-native-windows project.
So when the webview is loaded, it downloads static contents from web server to local cache folders.
But the webview cache folder is different from appx cache folder.
When I use react-native-fs function RNFS.exists() to judge if the web cache folder
(C:\Users\xxx\AppData\Local\Package\myproject\AC\) exists,
it catches an error that access denied.
I found a solution from microsoft website:
Adding
1) xmlns:rescap="http://schemas.microsoft.com/appx/manifest/foundation/windows10/restrictedcapabilities",
2) IgnorableNamespaces="uap mp iot rescap"
3)
to Package.appxmanifest.
But now the site http://schemas.microsoft.com/appx/manifest/foundation/windows10/restrictedcapabilities return error like
The resource you are looking for has been removed, had its name changed, or is temporarily unavailable.
How should I do to access other folders by RNFS.exists()?