This is okay. Modern apps that target recent enough api levels can do this.
I'd suggest you read through this part of the GrapheneOS website: https://grapheneos.org/usage#storage-access
A relevant part:
For modern apps, access to the shared storage is controlled in the following way:
- Without any storage permission, an app is allowed to:
- create media files in standard directories (audio in Music/, Ringtones/, etc, images in Pictures/ and DCIM/, videos in DCIM/ and Movies/)
- create files of any type (both media and non-media) in Documents/ and Download/
- create new directories inside standard directories
- rename/delete files that were created by the app itself
- rename/delete directories if it can rename/delete all files within those directories
There's a lot more info there, so I'd still suggest looking at that section of the website.