Cannot store files on Time Machine backup drive

I needed to format an external hard drive from Mac OS Extended (journaled, encrypted), the only available option was APFS.

On this hard drive, I had my time machine backup in Backups.backupdb and several folders with files, for example:

├── Backups.backupdb
├── Music
└── Pictures

With the new file system, I am not able to use the hard drive for both time machine and files at the same time. When I set it up for time machine backup, the drive is full with snapshots and cannot be modified by me (e.g., store files), for example:

├── Snapshot 1
├── Snapshot 2
└── Snapshot 3

Has this changed? How can I resolve this issue?

Solution 1:

You should not (and cannot) store files in the Time Machine volume. Instead, open Disk Utility and choose Add Volume on the disk. This allows you have a place to store files on the disk.

Volumes (unlike partitions) share space in the disk. Partitions reserve specific space on the disk and can't be easily adjusted. This isn't an issue with volumes.