Outlook - Online mode address book search fails with "Operation failed" when Name only is ticked.

This is narrowly isolated to the Address Book dialog’s Name only ANR search in classic Outlook online mode. Because More columns, Ctrl+K, OWA, safe mode, new profiles, other networks, and multiple machines work, this does not resemble an OAB download or local-profile problem. OAB troubleshooting primarily applies to Cached Exchange Mode, while your clients query the directory online. First check Microsoft 365 Service health for Exchange Online or Outlook incidents. Then record the exact Microsoft 365 Apps version, build, architecture, and update channel from affected machines, and compare with a supported build on one controlled test device. Run Microsoft’s Outlook diagnostics through Get Help and capture a reproducible UTC timestamp. If all users still fail, open an Exchange Online support case with the tenant ID, build, hybrid topology, ANR steps, and proof that More columns succeeds. I cannot confirm a published Microsoft issue for this exact Name only failure.