If you are unable to assign a new status to an issue, it may be due to a workflow permission setting.
To edit workflow permissions:
In the top menu, click on Your Avatar
Navigate to Administration -> Workflow.
Select your role in the project and the tracker being used for the issue.
If you would like to assign a newly-created status, clear the “Only display statuses that are used by this tracker” check box.
Click Edit.
Review and modify status transitions as needed.