With the latest Insider Preview build 18956, Microsoft made sideloading of MSIX apps obsolete. Now this format is fully supported by the OS, and works as a native executable format, the same way Windows 10 handles *.exe files.

With the latest Insider Preview build 18956, Microsoft made sideloading of MSIX apps obsolete. Now this format is fully supported by the OS, and works as a native executable format, the same way Windows 10 handles *.exe files.
MSIX is a brand new packaging format created by Microsoft. MSIX combines the features of the installer format used by Store apps and the classic MSI file packaging format. The new MSIX format supports all types of Windows apps including Desktop apps (Win32), .NET apps and Store (UWP) apps which used AppX.
During Microsoft's Ignite 2018 conference, the company shared more details about its brand new packaging format, MSIX. MSIX combines the features of the installer format used by Store apps and the classic MSI file packaging format. The new MSIX format supports all types of Windows apps including Desktop apps (Win32), .NET apps and Store (UWP) apps which used AppX.
Today, during the Windows Developer Day event, Microsoft has announced a new app format. The format is called "MSIX file". It combines the features of Store apps and the classic MSI file packaging format. The new MSIX format will support all types of Windows apps including Desktop apps (Win32), .NET apps and Store (UWP) apps.