Please put a check on Department Supervisor. Randomly set meetings with different employers and ask them to open up about their Supervisor. Give chance to your employees to grow within your organization. Get proper rational from Department Supervisor why he is not interested to get someone from his own team to grow.
Ensure all job postings should be open for internal employees. If Supervisor want HR to post job directly on Indeed or any other Job websites don't let it happen.
Treat your worker right