Hello,
Thank you for posting in Q&A forum.
Unfortunately, “Add Work or School account” option is only available in Windows Client OS instead of Server version.
REF: https://support.microsoft.com/en-us/account-billing/join-your-work-device-to-your-work-or-school-network-ef4d6adb-5095-4e51-829e-5457430f3973
In Windows Server Essentials, there's other option to manage user accounts. Please refer to below link for further details:
REF: https://learn.microsoft.com/en-us/windows-server-essentials/manage/manage-user-accounts-in-windows-server-essentials
Best Regards,
Hania Lian
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