M365 Copilot Chat (work) not working in Teams

The strongest clue is the license-assignment method: affected users receive Microsoft 365 Copilot through Okta, while unaffected users do not.
Start by comparing an affected user with a working user in the Microsoft 365 admin center, particularly the enabled service plans under the Copilot license and any provisioning errors.
Confirm that Microsoft Copilot with Graph-grounded chat is enabled, because a disabled or missing work-grounding entitlement could leave users with only the web-based Copilot Chat experience.
If the licenses match, compare Microsoft 365 Copilot app availability, Teams app permission policies, group membership, and Unified App Management assignments for both users.
Test any correction with one pilot user outside the Okta workflow first, then update the Okta license configuration before applying the fix broadly.