to Shut down, with the arrow next door allowing you to extend your options, like
restart or log off. It’s possible to customise this if shutting down isn’t the choice
you primarily use.
To do so, right click Shut down, select Properties and this will bring up a
taskbar customisation window that will let you choose your own power button
action. For example, you might want to default to sleep if that’s the choice you
usually go for.