External hard drive formatting

Bronxite57 wrote:

What formatting option should I use to format an external hard drive for use with time machine on iMac retina 4k 2017 running OS Mojave?

see: Which format to use: APFS or Mac OS Extended https://support.apple.com/en-us/HT208496

Are you preparing a Time Machine backup disk or bootable installer?
Choose Mac OS Extended (Journaled) for any disk that you plan to use withTime Machineor as abootable installer.

Mac OS Extended (Journaled), GUID scheme.

You're welcome.

I thought I said that.