Hmm. When I click the down arrow, it moves Layout panel up and down, but it does not take it back to the right side of the editor under Page Attributes.
Well when there’s more than 1 panel at the bottom, it seems there’s no way to drag them back to the side, I think it’s a WP Gutenberg bug which they need to fix.
The workaround is installing Classic editor plugin, once it’s activated, you can drag the panels to wherever you want, then you can disable or delete the plugin if you don’t need it anymore.