MSIX is native in Windows 10 1809 and above. There is a download to add it to 1803 and 1709 which is the equivalent. For Win 7 (and potentially other Windows OSs) Microsoft has announced but not delivered a solution. Details are sketchy, but I’d bet it ends up natively installing the MSIX package like it was an MSI. So, no MSIX Runtime, no PSF, no integration into modern things.