Read the Wikipedia pages for Microsoft Windows and its various versions for details.
Basically, Windows 11 is the "next version" of Windows 10 which is the "next version" of Windows 8.1, of 8, of 7, of XP, and of 2000, of NT 4, and of lower-numbered versions of NT. I've heard rumors, probably true, that at least some source code from the earliest versions of Windows NT is (with modifications) in Windows 11. That said, don't try to take any compiled applications from early-days Windows NT and run them on Windows 11. You CAN run some Windows 2000-era applications on Windows 11 though.
If you want to think of the newer versions as all just "upgrade versions" of the older versions, you can.
But if you asked Microsoft, they would say they are different operating systems.