Can't Access Photos
Photos are downloading to "Photos" from my phone, and I can see them in"Photos" on my Mac, but when I try to open or edit, I get a "!" and photo won't come up. When I try to move a photo to desktop, I get a "EXEC" icon.
Which system version is running on your Mac?
If your iPhone is running iOS 11 or iOS 12 and taking the photos and videos in the high efficiency HEIC or HEVC format, you need a Mac with macOS 10.13 or macOS 10.14 to be able to open the photos and videos. See this document on how to change the settings on your iPhone for more compatibility: Using HEIF or HEVC media on Apple devices - Apple Support
Alternately you can convert HEIC files to JPEG using the online converter at http://heictojpg.com/