A cloud-based identity and access management service for securing user authentication and resource access
That's correct, dynamic membership rules do not currently support the employeeType attribute. You have few options: create a static membership group instead, which you can periodically update via PowerShell/Graph API; use a different attribute if possible; if no suitable attribute exists, consider "copying" the value of employeeType to one of the extensionAttributeXX attributes, which are supported for dynamic membership rules.