I was confused with this when I first started using Obsidian, too. It can be closed by right-clicking the icon in the right sidebar. You can also move it to the left sidebar if it’s taking up too much space on the right.
In my case for the Obsidian Win10 version,
right-clicking on the left panel icon, does NOT show up a menu to remove the icon,
this make the same as left-clicking it!
e.g. right-clicking on the command prompt icon, will show up a screen to search for commands, followed by a list of available commands.