@m.kuijpers I am running into the same issue but I have not seen anywhere stated that arrays are not supported on Jira Server.
The documentation on entity properties for Jira Cloud and Jira Server (if arrays are supported) is super confusing (for reasons given here) and I have reported it to Atlassian already a couple of times.
I am still not sure if this is not a bug because like @m.kuijpers said this has been working on Jira Server so far…