flatpak is like a cross-distro snap that actually works. some of the apps are buggy at the fringes, but i've been opening issues to smooth them out. some of the apps like VS Code claim to be from microsoft, but are... unofficial?
Unless they have a verified checkmark next to the company/owner of the project it will be a 3rd party package of it. The name is mainly intended as a "This is from X" instead of "This is packaged by X" (unless you actually see the verified badge)
You are right. Besides proprietary app store, Snap lacks even basic sandboxing in non-Debian based distros. I can't believe that Canonical engineers thought this was a good idea when designing a cross platform packaging format.
Flatpak got everything right from it's initial design. Multiple repositories, Sandboxing that actually works in any Linux distro, OSTree to reduce disk space usage etc.