A couple of years ago we migrated from the 2008 to the 2012 version and we are currently in the process of trying to migrate our applications to that of 2019. We use Windows 10 for OS. We're researching z/OS, which is actually Linux based, to see how well it works with Windows applications.
When it comes to the SQL server, we have separate application and database servers, the latter which is also on Windows Server 2012. This means that we have a couple of applications in which we hosted in IIS and Windows Server 2012. Consequently, we have quite a collection of Windows 2012 that are currently running in our data center.
For the moment, we are not making use of the solution in our environment but looking into how we can have a license free OS that can both work with lower machines and function very well.