SSD + apfs Install option greyed out I'm sure I've seen this before, but I upgraded an older MBP (2011) to an SSD.  I boot to a High Sierra installer that i created and format it to Apfs, but then the drive is greyed out - it states it needs HFS+ to install.

Is this because this machine does not yet have the updated firmware that allows it to install on apfs?

Cheers
In some cases the volume has to be unmounted first.

Start the Mac in recovery. Select Disk Utility. Select the volume from the left. In the tool bar at the top of the main window click unmount. Now go the option to convert to APFS is no longer greyed out.