>Windows had a big, discontinuous shift when they abandoned the DOS-centric Windows codebase in the move to XP.
Windows 11 is the latest member of the Windows NT family, which originates from Windows NT 3.1 which coincides with Windows 3.1.
Windows NT 4.0, which coincides with Windows 95, is where things start to look more familiar to us today.
Windows 2000 followed to coincide with Windows 98 and ME and is where the NT family really got consumer-aimed software working right with the integration of DirectX all the way up to DirectX 9.
Windows XP which followed 2000 is really just 2000 with some more cleanup and QoL improvements. All the foundations were laid by the time of Windows 2000.
So yes, "all the 25 years of code" are definitely still in Windows 11 under a lick of paint.