I am not using an Asustore NAS, but did a search for SMB issues on Asustore and iPadOS and found this :
https://www.reddit.com/r/asustor/comments/1koetng/iphone_files_app_thinks_shared_folder_is_read_only/
Sorry to bump an old thread, but I hit the same problem with my SMB share. On macOS I could copy files just fine, but on iOS the folder always showed up as read-only.
What fixed it for me was adding the SMB domain to the username when logging in from iOS. So instead of just username, I had to use WORKGROUP\username. I hope that helps.
It is not the same, but might be related to the same cause in the Asustore Samba configuration, the page below is about a Samba ‘configuration’ issue :
https://nramkumar.org/tech/blog/2025/08/31/fixing-read-only-access-to-smb-shares-on-ios-18/
In iOS files app, you can connect to a SMB server over LAN and use it for storage (read and write). After an upgrade to iOS 18, it looks like Apple changed something where default settings for my samba server on Linux no longer allowed write access to the share from iOS – the share was always showing up only as read-only.
The fix is to add the following to the [global] section of /etc/samba/smb.conf:
vfs objects = streams_xattr
After this, run sudo systemctl restart smb and now you should have read/write access to the share from iOS devices.
If I read the Samba documentation regarding this settings, it makes sense :
The streams_xattr Virtual File System (VFS) module enables applications to store information in Alternative Data Streams (ADS). Certain applications, such as the Microsoft Edge browser, require ADS to operate correctly. For example, if you use Edge to download a file to a Samba share that has no ADS support enabled, the download will fail.
Samba stores ADS in the user.DosStream.ADS_name extended attribute of a file or directory. Therefore, the file system of the share must support extended attributes. For details, see your operating system’s and file system’s documentation.