It seems like the new defender portal is missing some features when you have a Business Premium + MDI addon license only. For instance the Assets->Identities section described in the doc here is not present:
Microsoft Defender for Cloud Apps in Microsoft 365 Defender (Preview) | Microsoft Docs
Additionally when creating custom detection rules the "user action" section is also not present (which should allow you to disable users onprem with MDI), I think the new portal assumes that if you don't have a defender for cloud apps and/or AAD P2 license that these features must be hidden. But these features also make part of MDI which leaves the new portal experience broken with this license combination. And this is not highlighted at all in the current docs.
