Click on the“Change settings that are currently unavailable". then only you will be able to make changes in the "Password protection on wakeup" and "Shutdown settings" sections.
After enabling Hibernate Click on Save Changes. Now Hibernate option will be available along with Shut down & Restart.
Additionally you can Hibernate your machine by simply running Shutdown -h command. To Hibernate your PC using above command, press Win+R (i.e. open Run prompt) & enter Shutdown -h and press OK to Hibernate your PC.