This is how TM works with a networked drive it creates a sparsebundle on the network drive, and then mounts it. Time Machine can work on 'foreign' drives fine by using a sparsebundle disk image.
PARTITION EXTERNAL HARD DRIVE FOR MAC AND WINDOWS MAC
Yes, you can use a single NTFS disk for both Windows and Mac backups.
![partition external hard drive for mac and windows partition external hard drive for mac and windows](https://jasoncoltrin.com/wp-content/uploads/2016/05/PC-Mac-External-drive-format-3-1280x720.png)
My external 1 TB drive, which I use for backing up my Mac and my wife's Windows PC, has two partitions called "Time Machine" and "BACKUP_WINDOWS": Replace BACKUP_WINDOWS with the NTFS partition name.
![partition external hard drive for mac and windows partition external hard drive for mac and windows](https://i.ytimg.com/vi/qc9VnF-QIdY/maxresdefault.jpg)
To prevent the NTFS partition from being mounted every time you connect the drive into your Mac add this entry to /etc/fstab (as explained here): LABEL=BACKUP_WINDOWS none fusefs_txantfs noauto When you're done, plug the drive again into every Mac/Windows computer and select the corresponding partition as backup drive (see here for OS X and here for Windows).
![partition external hard drive for mac and windows partition external hard drive for mac and windows](https://www.techadvisor.com/cmsdata/features/3369574/how-to-read-apfs-drives-in-windows_thumb1200_16-9.jpg)
Your preferred setup is not possible: OS X can't share an NTFS disk with Windows for backup because Time Machine needs HFS+ (from ):