On prem Outlook has a limitation as below:

https://help.webex.com/en-us/article/n194fs/Known-issues-and-limitations-for-the-Webex-Scheduler-for-Microsoft-Outlook

You might not be able to schedule meetings for other hosts using a shared folder (delegate scheduling) in Outlook for Windows. The options appear dimmed due to a Microsoft on-premises Exchange limitation. You can still schedule Webex meetings for others using their Webex host account with the Webex Scheduler. If you schedule meetings for other hosts, the Outlook meeting invite appears to be from you instead of the host you scheduled the meeting for. The host that you schedule the meeting for doesn't receive a meeting invite in Outlook unless you add them as an attendee in Outlook


This feature is really important and the customer is looking to implement this for on prem.