I have a MacBook Pro (13-inch, Mid 2010) with a 500GB spinning hard disk boot drive with High Sierra 10.13.6. Disk Utility reports the drive as "SATA Internal Physical Volume - Mac OS Extended (Journaled)". I ran First Aid on it and it came back good.
I have a 500GB SSD in a USB enclosure.
I booted into Recovery and started Disk Utility. I erased the SSD and chose plain APFS format (the four options available are all APFS variations). I tried restoring to the SSD, but the Restore window shows "None Available" in the "Restore from:" drop-down.
I read something that suggested converting the boot disk to APFS, but that menu item is grayed out when I select that drive.
How can I get the contents of this spinning hard drive onto the SSD?