MS 365 Outlook move toolbar to bottom

Use Outlook Settings to Move the Toolbar to the Bottom.
You toggle an option in settings, and that shifts the toolbar from the left sidebar to the bottom bar.

-To do that, in your Outlook app’s top-left corner, click "File."
-From the left sidebar, select "Options."
-On the "Outlook Options" window, in the left sidebar, click "Advanced." On the right pane, turn off the "Show Apps in Outlook" option.
-Save your changes by selecting "OK" at the bottom.

Outlook will display a prompt that says you need to restart the app to bring your changes into effect. Do that by closing and reopening your Outlook app, and your toolbar will sit in the app’s bottom bar. And that’s it.