> Unverified Flatpaks are disabled by default.

> They are not officially approved by the developer of the application and could be maintained by anyone.

https://blog.linuxmint.com/?p=4719

Ah, I said it would happen...

Flatpak broke the separation of powers between developers and distribution packagers with this new "unverified" flag.

Both does not share the same incentives. That is why packaged softwares, provided by your distribution, are safer.