Windows 2000 is Windows NT 5.
Before that, there was Windows NT 3.1 (the first version), NT 3.5, NT 3.51 and NT 4.
Windows 2000 was the fifth version of Windows that did not need DOS.
And as Windows NT was a pure 32 bit OS, where the Dos based Windows were 16/32 bits.
Windows NT was designed by Dave Cutler and released from July 27, 1993.
https://en.wikipedia.org/wiki/Windows_NT
By that time there were already 5 editions of Dos based Windows: 1/2/3.0/3.1/3.11.
The first Dos based Windows was released much earlier: November 20, 1985
https://en.wikipedia.org/wiki/Windows_1.0x
To add to the confusion there were a Dos based Windows 3.0 and 3.1 and a Windows NT 3.0 and 3.1.
Your claim is wrong. You said that the first Windows not based on DOS was 2000; that is not true. The first Windows not based on DOS was in 1993.
What name Microsoft marketing put on it is irrelevant. If you opened a command prompt on Windows 2000 and typed `ver`, it said Windows NT 5.0.
Do not get misled by branding. As Terry Pratchett said:
"Zoon tribes are very proud of their Liars. Other races get very annoyed about all this. They feel like the Zoon ought to have adopted more suitable titles, like ‘diplomat’ or ‘public relations officer.’ They feel they are poking fun of the whole thing." - Equal Rites
Marketing means lying. Marketing took the letters "NT" out of Windows 2000's name, but that does not mean it was the first product of its kind. It was not. It was the fifth.
BTW I used Windows 1.1 on a PC XT. At the time, my employer wanted to use computers to teach employees technical subjects (adult education). My employer was Direction Général des Télécoms (now Orange) and the department was DFPT (in Montpellier/France) (I am 65 yo).
When I saw what was needed to just program a window with a simple text I was horrified. In DOS just a few lines were enough, on Windows 1.1 it was several hundred of lines!
My company much later used software such as Macromedia to make computer based learning. It ran on (Dos based) Windows 3.11, I think (but I am not sure ) that is was DOS 4 or maybe 5.
