Serg
From https://grapheneos.org/usage#storage-scopes:
This means that the app can't see any of the files that were created by other apps. The app is still allowed to create files and directories, same as any other modern app that doesn't have any storage access permission.
If the app requests the "All files access" permission ..., then the write restrictions that are normally applied to apps that don't have a storage access permission are relaxed to provide the same write access that the app would have if it was granted the "All files access" permission. This is done to ensure compatibility with apps that, for example, create a new directory in the root of shared storage.
So yes, it can create folders and files anywhere, but only read/edit/delete what it has created itself, and things in the folder you allowed.