Well, the build in flathub is mantained by random people with no official affiliation to Anki and/or Damien, not even recognized as an official distribution method by him, so I don’t think it should be verified.
Damien still only recommends downloading it from the website.
That being said, the flatpak package has been my main method of using Anki for ages now, it works perfectly, it integrates with my package manager, you can control premissions, I think it’s great. I’ve already defended it here that Anki should addopt flatpak as an official distribution method.
I’m afraid I don’t feel comfortable adding an ‘official’ label on something that I’m not reviewing before releases go out. And while I know that quite a few people are using the flatpaks successfully, there are still some bugs that they have that are not present in the official packages.