APFS

APFS format is unavailable if partition scheme is Master Boot Record or Apple Partition Map. Use GUID and then choose APFS.

Boot to your Recovery HD, Restart while pressing and holding the Command and R keys.

Open Disk Utility, click on View in the menubar and select Show All Devices.

Now click on your HD in the left column and click on Edit and see if you can select Convert to APFS.

If that is not available I am all out.

rickall wrote:

How do I format an SSD drive as APFS with Mojave 10.14.6? It is not a choice in disk utility . Thanks

Apple provides non-destructive methods for start-up disk drives for APFS conversion, and hence no data (files or folders) will be lost. On the other hand, APFS formatting will erase all the files and folders stored on the external hard drive. If not backed up earlier, APFS formatting on the external drive will cause data loss. Even with the start-up drive, one may delete or lose files from the APFS formatted media.

Non-Destructive APFS Conversion

Restart the Mac into Recovery Mode.

Launch Disk utility.

Click-select your named boot volume—the default name is "Macintosh HD" —(Not the physical drive above it.)

In the Disk Utility> Edit menu> select “Convert to APFS"

It has been awhile since I ran the conversion myself, but maybe you can report back—

but my understanding it is the The Physical drive it is the GUID partition map and it is "Macintosh HD" you want to convert .

Always advised to have a current redundant backup plan before any update/upgrade/conversion—only in this way can you restore your User if something goes UN-expectantly sideways.