Isn't MSIX packaged apps on Windows basically the same?

They will even list all the capabilities before installing, and I believe it can handle auto updates outside the MS Store as well.

But I think the main issue is that you can't give granular permissions. I would like to make my own sandbox rules, like only enable a single domain for networking for the app, only allow specific folders, etc.

I don't think you can get this granularity on macOS/Windows right now.