Hide background in photos

There is no means to hide a background within Photos on macOS, though image editing tools can help with selecting and editing images.

You can potentially use Photos to select the subject too, if your Mac can be upgraded to macOS 13 or later:

Isolate and copy a photo’s subject in Photos on Mac - Apple Support

With the Ventura system there is a built in feature of the Finder under Quick Actions that will remove the background of a photo. Here's an example:

If you aren't running Ventura you'll need a 3rd party image editor like Adobe Photoshop Elements, Gimp or GraphicConvereter.