Hi @Kevin Boteler,
Welcome to the Microsoft Q&A and thank you for posting your questions here.
- Verify HNS is enabled on the storage account.
- Confirm tenant/subscription match between the Synapse workspace and the storage account.
- Assign/confirm Owner + Storage Blob Data Contributor on the storage to you and the Synapse workspace principals.
- Temporarily relax network restrictions (or configure managed identity access) and retry the picker.
- Refresh portal session (InPrivate / different browser) and re-open the creation/link blade.
- Recheck resource provider registration.
- Please try using a different region.
If the issue persists, please share the required details in a private message.