Seagate back up plus on a mac

For the various locations and Macs I deal with, I use a mix of Seagate external hard disk drives and Synology NAS storage servers for the site-local local or network-local Time Machine backups.

Not the Seagate software, though.

My comments were generic to how Time Machine works, and to how Time Machine reacts to full backup devices. Sometimes poorly.

Time Machine backs up all local storage contents, including local photos and videos if you’re not using iCloud for photos and videos.

If you are using iCloud for photos and videos, Apple has a separate sequence for archiving that data locally:

Archive or make copies of the information you store in iCloud - Apple Support

Mixing Time Machine and other usage on the same device is possible, but can be problematic, and wouldn’t be my choice.

Get another storage device for that.

It is never a good idea to keep data and backups of the data on the same drive. If the drive fails you've lost your data and your backup.