While we’re close to the end of Skype for Business Online (retiring 31st July 2021), Skype for Business server lives on for those who want/need it, with Skype for Business Server extended support until 2025 and Skype for Business Server 2022 confirmed.
One challenge Skype for Business Server has is that its control panel uses Silverlight technology, which will reach the end of support on October 12, 2021. Silverlight development framework is currently only supported on Internet Explorer 10 and Internet Explorer 11 as Microsoft move to Chromium Edge this support goes away too.
Microsoft has been working on and releasing a new Modern Admin Control Panel (MACP,) based on react, in phases since July 2019. It is now general availability as part of the Skype for Business Server 2019 March 2021 Cumulative Update.
Check out more details in the blog from Microsoft here.