The sandboxing part isn't quite true anymore. You can use Desktop Bridge to package win32 apps for the store. These apps are not sandboxed in the way that UWP apps are though they are still kinda-sorta sandboxed (they can access any file the user can, but the appdata folder and registry edits are sandboxed).

There is also some sort of vaguely-stated plan to allow totally unsandboxed win32 apps in the store at some point in the future but seems to specifically only apply to games.

https://docs.microsoft.com/en-us/windows/msix/desktop/deskto...