When unmounting USB devices in use, it says "One or more files on this device are opened in application <application>" but with NFS shares, it just says "you are not authorized to remove this device". Please add descriptive USB device information to NFS shares.
STEPS TO REPRODUCE
1. mount NFS share
2. open file on NFS share
3. try to unmount NFS share in device manager
(available in About System)
KDE Plasma Version: 5.15.5
KDE Frameworks Version: 5.60.0
Qt Version: 5.12.3
Information needs to be added in Solid AFAIK.
A possibly relevant merge request was started @ https://invent.kde.org/frameworks/solid/-/merge_requests/22
Git commit ad66f5e6a35dba54bff1f9eddb955c741af16e97 by Méven Car.
Committed on 02/12/2020 at 06:17.
Pushed by meven into branch 'master'.
FstabBackend: return DeviceBusy where umount failed on EBUSY
M +6 -2 src/solid/devices/backends/fstab/fstabstorageaccess.cpp