Sometime back, we saw how to Share the classic site to External Users, and in the same manner, we cannot see the Modern Sites listed on the sharepoint admin portal. Hence, let us see, how to enable this at the tenant level.
The tenant level settings are as shown below.
1. Login to the admin portal of Office 365 tenant. https://admin.microsoft.com/AdminPortal/Home#/homepage
2. Select the Services and Add-ins under the settings tab.
3. Select the Sites on the right side panel.
4. Based on our requirement, select the options from the below screen.
5. Now, go back to the Modern site and go to the URL https://<<TenantName>>.sharepoint.com/sites/ModernSiteCollection/_layouts/15/groups.aspx
6. Add the External Users here. We can invite the people who has a valid Microsoft ID. (either a different tenant id, Hotmail, live, outlook ids etc.,)
7. After that, they should be able to access the site.