You can add all SharePoint Online sites in the tenant, all SharePoint sites that are associated with Microsoft Teams, or all project web app sites to a SharePoint Online app.
Note: To associate all Project Web App sites as content, disable Modern Authentication. You can back up Project Web App sites only in a basic authentication environment.
From the navigation pane, go to Protect > Office 365.
The Office 365 apps page appears.
In the Name column, click the app to add the template to.
The app page appears.
On the Content tab, click Add, and then select the category of sites that you want to add.
The Edit association dialog box appears.
From the Office 365 plan list, select the plan to use for the sites.