I added a property to the Done status for the project workflow, i.e., jira.issue.editable = false
However, I discovered that the Assignee field could still be changed when the status is Done, see below.

Before adding the property, jira.issue.editable, to the Done status, I could change the other fields, e.g., Description, Reporter, Story Points, etc. After I set the above property to false, all the aforementioned fields changed to read-only except for Assignee.
Although I was logged in as the organization admin, which could explain why I was able to modify it, but is there a way to make the Assignee read-only after the issue is Done?