In case you didn’t know, Microsoft Demos (demos.microsoft.com) has been migrated to the new Customer Digital Experience platform (cdx.transform.microsoft.com).
In this new platform, new tenant types are introduced which let your create cusom type tenant for a period of 90 days to 1 year.
To create a new tenant, head on ever to https://cdx.transform.microsoft.com then select My Environments.
Select Create Tenant
Specify the type of tenant, period, tenant location, and content packs and you’re good to go.