Windows 8: https://www.microsoft.com/en-us/software-download/windows8

Windows 11: https://www.microsoft.com/en-us/software-download/windows11

Windows 10: https://www.microsoft.com/en-us/software-download/windows10

Windows 7: https://www.microsoft.com/en-us/software-download/windows7

note: Windows 7/8 ISO is no longer provided by Microsoft. If you still want to use 7/8, you have to download the ISO from a 3rd party source.