Photos isn't allowing me to email photos

Scenario:

I've selected five photos to email. I hit "share" and get two options: 1) iCloud Photo Sharing and 2) More...

"More..." gives me the Extensions window. Mail is in the list and check marked, but ghosted.

If I drag my photos to the desktop, they turn into an HEIC file and are good for nothing. I don't even know what HEIC is.

How do I work this out???

I realize I clicked that this is happening on my 27" iMac, but I'm actually currently working on my 2011 21.5". I'm not allowed to update that portion of my request.