Shutdown after render is a Blender add-on that powers your PC down automatically once a render completes. Its controls live in the Render Properties tab, at Properties > Render > Shutdown after Render, and you switch the function on with the Power icon at the top of the panel.
A Shutdown-Type dropdown sets what happens when rendering ends. Shutdown, the default, turns the PC off completely; Hibernate shuts it down while remembering the state of open applications so they reopen at next startup; and Quit closes Blender. The commands behind shutdown, hibernation, and canceling the shutdown can be customized in the add-on's preferences.
Because Blender does not save rendered stills to the output folder automatically the way it does with animations, the add-on adds a Render Image to Disk button in the render top menu. It renders the active scene and then saves the image to the path set in Output Properties. The add-on is compatible with Blender 4.2 LTS and newer and needs no special permissions.