How do I delete Multiple photos in Photo?

Select the multiple thumbnails as you would in iPhoto or the Finder. Then use the key combination of Option+Command+D to move the photos to the Recently Deleted album.

Go to the Recently Deleted Photos album via the File ➙ Show Recently Deleted menu option. There you can finish the deletion process or let Photos do it in 30 days which gives you time to change your mind is you're so inclined.

Where in the library are you trying to select the thumbnails? In an album, the All Photos window, the Photos window, where?

You should be able to hold down the Shift key and click on two thumbnails and get all of the thumbnails in between selected. If that doesn't work first reboot, open Photos and try again. If that fails repair the library according to this Apple document: Repair Your Library and try again.

Are you able to select and delete from anywhere else in the library?

Now if Apple is so good at handling pointers (via smart albums, etc.) why can't it handle deletes from "last import", smart albums etc. I wouldn't think it takes a genius to manage that.

The problem you're having is limited to your particular situation. You're the first and only to have this particular problem.

As a test launch Photos with the Option key held down and create a new, test library. Import some photos and test to see if the same problem persists. Does it?

Yes from the main Photo (or root). Now if Apple is so good at handling pointers (via smart albums, etc.) why can't it handle deletes from "last import", smart albums etc.

There must be a problem with your Photos library.

When I select multiple photos from "Last Import", a smart album, or an album and use the key combination ⌘⌫, the photos are deleted and moved from to the "Recently Deleted" album, where I can deleted them completely from the library.

Have you modified the bindings of your keys in the System Preferences > Keyboard > Shortcuts panel?

Check the bindings of the keys there.

Which version of MacOS X and Photos do you have?

To check, if the problem is caused by your Photos Library or is more general, create a second Photos library just for testing. Import a few photos, then try to delete them from your Last Import album. Does this work in your test library?

If it does not work in any library, it might be a problem of corrupted cached files in your user library.

To check for corrupted preferences or caches try, if trashing the preferences file helps:

I'd delete the complete folder ~/Library/Containers/com.apple.Photos/ from your User Library and restart the Mac, then try again.

Your user library may still be hidden.To reveal the hidden User Library:

• Bring the Finder forward by clicking on the Desktop or the Finder icon in the Dock.
• Select your user/home folder (with the house icon in the Finder sidebar)
• With that Finder window as the front window, press the key combination ⌘J to bring up the View options.
• In the View options panel enable ’Show Library Folder’. That will make your user library folder visible in your Home folder.
• Open your Home folder, then the Library folder, then Containers.
• Move the complete folder ~/Library/Containers/com.apple.Photos to your desktop. Move the entire folder, not just the contents.

Now restart the Mac and try again. If all is well, delete the folder from the Desktop.