I don't have any coding experience, but I have created an issue that outlines the Android 11 permission issue. Hopefully someone can help! https://github.com/mayallst/MusicBeeWifiSync/issues/6
It appears permissions for MANAGE_EXTERNAL_STORAGE is neededhttps://developer.android.com/training/data-storage/manage-all-files
However, looks like that may be difficult given restrictions on apps requesting these elevated permissions:
"You should request the MANAGE_EXTERNAL_STORAGE permission only when your app cannot effectively make use of the more privacy-friendly APIs, such as Storage Access Framework or the Media Store API. Additionally, the app's usage of the permission must fall within permitted uses, and must be directly tied to the core functionality of the app. If your app includes a use case that's similar to the following examples, it's likely to be allowed to request the MANAGE_EXTERNAL_STORAGE permission:
Backup and restore apps
Document management apps
On-device file search
Disk and file encryption
Device-to-device data migration"
I don't think it'd be feasible to ask the Gonemad dev to save the backups to the shared media locations since that information is not media, and this would fall under the 'Device-to-device data migration' use case mentioned in the list above. May just be as 'simple' as a little permissions tweak. I put that in quotes only because I'm not sure what that entails...