As of March 1, 2023, in LinkedIn Recruiter and LinkedIn Talent Hub, Microsoft integrations will only work with cloud deployments. Microsoft will no longer allow Hybrid Deployments to access calendar and mailbox APIs.
Hybrid means that exchange runs on a server that's physically present at your office and that server has a connection to Microsoft's servers to support use of the API. Cloud means that everything runs on Microsoft servers.
Microsoft support for mailboxes
The End of the REST API for On-Premises Mailboxes Preview