In order to restore a course with enrolled users from another Moodle site into a Moodle Workplace tenant, the capability "moodle/restore:createuser" is needed. The capability can not be added to a tenant administrator. The problem: Tenant admin can therefore not restore courses with user data.
So workaround is to assign a system role with that capability to the tenant administrator. Problem: Users are created, but not as tenant users, so tenant admin basically has problems to deal with these users (can not see user details, they are not in the list of tenant users, etc.)
Workaround 2: Upload users before restoring the course via CSV. That turns out to be very complicated. Maybe it works, if all users of a site are restored, but it is not possible to filter user by course enrolments.
Basically: Restoring a course to a tenant with user data is not possible. Also migrating a site to a tenant is thus very complicated.