Office 365 allows everyone in your organization to work anywhere and at any time. However, it is your responsibility to back up all business-critical data, including Exchange Online, SharePoint Online, OneDrive for Business, and Microsoft Teams.
Many people believe that Microsoft O365 includes backup. But read the fine print!
“We strive to keep the Services up and running; however, all online services suffer occasional disruptions and outages, and Microsoft is not liable for any disruption or loss you may suffer as a result. In the event of an outage, you may not be able to retrieve Your Content or Data that you’ve stored. We recommend that you regularly backup Your Content and Data that you store on the Services or store using Third-Party Apps and Services” –
(6b. Service Availability)