There are several solutions for your reference to address the unmount issue:
1. Install third-party NTFS tool for Mac, iBoysoft NTFS for Mac. This software provide full read and write access to NTFS-formatted drives on macOS.
Best NTFS for Mac by iBoysoft
2. Open Terminal and type the following commands to manually mount the drive:diskutil list
Identify the identifier for your NTFS drive (e.g., disk2s1) and then try:sudo mkdir /Volumes/NTFS_Drive
sudo mount_ntfs -o rw,auto,nobrowse /dev/disk2s1 /Volumes/NTFS_Drive
Replace /dev/disk2s1 with the correct identifier and NTFS_Drive with your desired mount point name.
3. Check for macOS updates and keep your macOS updated to the latest version.
4. If possible, reformat the external drive to a file system natively supported by macOS, such as exFAT, which is compatible with both macOS and Windows.
5. Use Disk Utility to verify and repair the disk. Open Disk Utility, select your external hard drive and run First Aid.
6. If these solutions do not work, consider contacting Apple Support or checking forums for any newly suggested fixes specific to your case.
You can also refer to NTFS External Drives Not Mounting/Working on Mac
