Hi @Machia, Tina ,
What's the specific version of your Outlook client(File>Office account>About Outlook)?
According to my experience on my Outlook 365 Version 2111(Build 14605.2000) Beta Channel, the navigation bar would be moved to the left side when I turn on the Coming soon option, which is same with yours.
Based on the feature introduction, I think it's designed to access and switch to other Microsoft app more easily(such as Microsot Todo), for more information, you could click the coming soon button in Outlook.
Actually, the "coming soon" option in Outlook is an opportunity to preview new features at your convenience and share your feedback with us before we finalize the change for all customers. If you have any suggestion about this feature, it's recommended to submit a feedback under this feature(click coming soon button>Slide to the bottom>choose "Yes" or "No" under the question). Your time would be highly appreciated.
If you don't want to work with this new feature now, please turn off coming soon by click the option next to "coming soon" like below(from on to off) in the upper right corner of Outlook and restart your Outlook client to check.
Hope that would be helpful to you.
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