Depending on how you count them, there have been 15 major versions of Windows, with Microsoft's inconsistent naming scheme resulting in the current version of Windows being Windows 11—go figure. A lot ...
Growing up using a PC that ran on Windows 3.1, I don't think it ever occurred to me that there was a Windows 2.1. Or 1.0. That was just Windows, until Windows 95 came around a few years later. But ...