@Richard Infield - Thanks for the question and using MS Q&A platform.
Note: Don't see the latest updates in the Microsoft Purview portal yet? The newest updates will be available shortly for your organization as the global update progresses.
Why will Purview search issues available in New portal?
Here is the update from internal team: I would suggest you to use Classic Purview Portal untill we complete migration experience from the classic to the new portal. Purview search in Microsoft Purview portal will be coming shortly. We don't have ETA and I will be updated this thread once it's available.
For more details, refer to Learn about the new Microsoft Purview portal (preview).
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