Microsoft has added a lot of sidebar applications to its Mail applications. The addition of sidebar applications is a shortcut to common office software components.
For example, when you open the mail application, you can see the Word, Excel, and PowerPoint icons on the left, and click to quickly open the corresponding components.
Perhaps Microsoft thinks that users can quickly open the office suite to record content when checking emails, but of course, it can also be regarded as Microsoft’s way of promoting office software.
If users do not install these office components, they will be redirected to the Microsoft 365 purchase page. Microsoft prefers users to purchase personal or family subscription versions.
 Mail is getting "Open Words", "Open Excel" and "Open PowerPoint" pic.twitter.com/pT8qCZppRA
— Aggiornamenti Lumia (@ALumia_Italia) November 23, 2020