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

If you need installation Instructions..

1. Download the Extension from the above link like this.
   

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.