Photo editing

The Photos.app does not have editing brushes, and it is not possible to apply adjustments just to the edges. Only the retouch tool can be applied locally. The best you can do in Photos make it look less sharp is to reduce the overall contrast. Use the slider in the Light section of the adjustment tools.

You will have to use an external editor to soften or blur edges.

A quick way to soften an image is to use an Automator service to apply a quartz composition filter. You can apply effects to photos you have exported to a folder in the Finder.

To create an Automator service:

• Launch Automator.
• Create a new Quick Action (on Catalina) or a Service, when using an older system version.
• Drag a "Get Selected Finder Items" action from the library into the workflow pane.
• Drag an "Apply Quartz Composition Filter" action from the library into the workflow pane.
• Set the filter to "Blur" and adjust the slider for the amount.

Save the Service with a suitable name. Select an image file in the Finder and and use Quick Action menu in the Finder to run the Quick Action (or the Touch Bar, if your Mac has a Touch Bar) and watch your photo to become softened.

If Automator does not show the Quartz Filters, you may need to install the Developer Tools.

But most image editors are offering smoothing or blurring filters, for example Graphic Converter or Luminar.

Today it does not seem to be possible to edit a post. Sorry for the many add-ons:

• Enable "Options > Show this action ...". This will show the "Amount" Slider when the workflow is running.