Lightroom Classic: On May 2 2018 I updated my MacBook Pro (v10.13.4) with Security Update 2018-001 I can no longer imports photos, etc.

Well, that would depend on the cause of the problem. What happens when you try to import photos? And where are you trying to import them to?

If I try to import photos, from a memory card from my camera or from an external hard drive on my MacBook, no images are shown in Grid view and the Import button is grayed out.  Where I'm trying to import to doesn't seem to matter as an option.