Flash Player MSI installer is available with a Flash Player distribution license agreement. See Adobe Flash Player Distribution | Adobe for more information. For the vast majority of use cases Flash Player distribution license is free.
Note that Microsoft embeds Flash Player in IE on Windows 8.1 and 10, and on Edge browser in Windows 10, and all updates are released by Microsoft via Windows Update. The ActiveX MSI installer will not run on Windows 8.1/10.