GOSling it doesn't seem to request any kind of storage permission, so storage scopes isn't listed.
I just tried the app out and it is working without any issues for me. I was able to save multiple notes. I can't find the files later, so I'm assuming the app is saving them in the app's internal storage folder (see https://grapheneos.org/usage#storage-access).
Under what circumstances are you getting this error? Maybe triggering it will help me or someone else help figure out what the issue is.