apple file system and mac os extended

If you are using the external drive only for data storage, then use MacOS Extended (Journaled). APFS is a new file system that tends to have issues that Disk Utility is not able to repair which then requires erasing the whole drive. If you are going to use the external drive as a macOS boot drive for macOS 10.15+, then you will need to use APFS.

If you are using the external drive for a Time Machine backup, then I will have to defer to other more knowledgeable contributors since I don't use Time Machine. I know that at least until macOS 10.15, that Time Machine required a MacOS Extended (Journaled) external drive. I think macOS 11.2.3 Big Sur allows the use of APFS for a Time Machine backup drive now. Personally I would still use MacOS Extended (Journaled), but there is always a chance a newer version of macOS or Time Machine may require a Time Machine backup drive to be formatted with APFS.

Hi,

If you are using High Sierra or newer macOS, you'd better choose Apple File System.

Then the first paragraph of my previous reply applies to you (specifically the first two sentences).

You should always have frequent and regular backups of your computer and any external media which contains important & unique files.