If it’s blank, you’re not using NFS to access the shared folder.
You’re using SMB and all files written over that SMB connection have the UID/GID of the username used to mount with (SMB credentials)
On the Linux host -
When you use NFS, you will preserve the UID/GID from the Linux side if so configured to do so in the NFS export rule on the Syno (which is the norm)
