If you need to create a site collection that uses a classic template, you can navigate to the classic SharePoint Admin Center page by manually typing in the URL and selecting the Classic site collections page link under the Classic features section of the new SharePoint Admin Center or by using the Microsoft 365 Admin Center. In this example, you'll follow the Classic site collections page path. The steps are identical once you get to the classic site collections page:

1. Navigate to the SharePoint Admin Center (https://tenant-admin.sharepoint.com).
2. In the navigation pane, select Classic features:

3. On the Classic features page, expand More classic features:

4. Select Classic site collections page. This will open a new tab in the browser:

5. Click New | Private Site Collection:

6. Fill out the New site collection page details by entering values in the Title, Web Site Address, and Administrator fields. Select a template in the Template Selection area, and select a time zone for the site collection in the Time Zone area. Click OK when finished:

Once the site creation process has finished, you can navigate to the site and begin to customize it.