Microsoft Entra ID Tenant Choices
Dedicated Tenant for TRE
We recommend that you have a dedicated Tenant for your TRE rather than using your corporate tenant. This is because TRE is able to automate some of the AD Tenant Admin tasks for you. In order to do this, there is an Admin User that has the ability to create AD Applications. This would not be normal for a Corporate Tenant.
Users from your corporate tenant can be guested into this new TRE tenant.
Corporate Tenant
It is possible to use your corporate tenant for TRE. This does have the advantage of only managing a single tenant, but your Microsoft Entra ID Tenant Admin must be aware of what TRE brings to your organization and must be prepared to carry out some admin tasks, like creating an Microsoft Entra ID Application every time a new Workspace is created.
Create Dedicated Microsoft Entra ID Tenant
Follow this guide to create new dedicated tenant.