Power Off button is gone on Ubuntu 20.04 LTS

You may use this extension which brings out the submenu and rearrange the order.

Bring Out Sub Menu Extension

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If you need installation Instructions..

  1. Download the Extension from the above link like this.
    enter image description here

  2. Go to the downloaded location/Directory/path.

  3. Right-click in the empty place and click "Open in Terminal"

  4. run the command

    gnome-extensions install BringOutSubmenuOfPowerOffLogoutButtonpratap.fastmail.fm.v5.shell-extension.zip
    

    (Note that tab completion is available, you dont need to type entire file name, Just type "BringOut" and hit tab)

  5. Refresh the gnome-shell with "Alt+F2 r" Enter method.

  6. run the command

    gnome-extensions enable [email protected]
    
  7. Refresh the gnome-shell with "Alt+F2 r" Enter method.

Now you will see the submenu out of it and merged with system menu.