Add a contact bar
I work for a company with 40K employees. Lotus notes sametime had a contact bar on the side that allowed you to group contacts by department, and displayed who was online facilitating communication with the right people in the right department when it was needed.
This has been the biggest pain point that thousands of our employees have gripes about with the migration to Microsoft teams. Don’t get me wrong, teams has some great features that blow sametime out of the water, but most of us would gladly give all those up for the contact list back.