I think I tried one of those alternative app distribute-y things at the time, but I don't remember which, and I came away disappointed. If memory serves, I couldn't establish whether it actually did any sandboxing, or what it did by default (like intentionally opening up this exact hole), and certainly not how to configure it, and gave up shortly in favor of something I'd at least seen before.

It might have been Snap. I don't like Snap.