WhatsApp

You can use the Share option, to AirDrop the Photos to your Mac, and then import them to Photos.

Link->How to use AirDrop on your iPhone, iPad, or iPod touch - Apple Support

You can save them to the Photos App on your iPhone and then import them to the Mac:

Link-> Import photos from a camera or phone using Photos on Mac - Apple Support

Or if you are using iCloud Photos, you can simply save them directly into the Photos app on your iPhone and they will sync to Photos on the Mac directly through iCloud.

Link-> Set up and use iCloud Photos - Apple Support

O.k, so open the photo in WhatsApp, click on the downward arrow at the top right of the screen This will download the photo to your downloads folder. Then simply use the Import function in the Photos App->File Menu to import the photo into Photos.

Or if you have the Apps side by side, just drag the photo directly from WhatsApp into the Photos app.