Syncing your account to the Microsoft Cloud means that a copy of your email, calendar, and contacts will be synchronized between your email provider and Microsoft data centers. Having your mailbox data in the Microsoft Cloud lets you use the new features of the Outlook client (New Outlook for Windows, Outlook for iOS, Outlook for Android, Outlook.com, or Outlook for Mac) with your non-Microsoft account, just like with your Microsoft accounts.

https://support.microsoft.com/en-us/office/sync-your-account-in-outlook-to-the-microsoft-cloud-985f9e19-d308-4e85-9d1d-0c6f32f8e981?ui=en-us&rs=en-us&ad=us#OfficeVersion=New_Outlook_for_Windows

Outlook for Android (and I believe iOS) has done this for years already.