I would argue that it depends a lot on what kind of beginner you have. If you have someone that only uses basic desktop PC functions, like browser, email and maybe stuff like video, photos and documents. You can set it up once, and then have a system that updates itself reliably and has minimal maintenance overhead and isn’t easy to break.

In my experience that system is more robust and gets updated than a generic Debian system.

Of course there are downsides, and those include issues caused by apps running inside flatpak, like system themes are disrespected, opening files in one app, doesn’t respect the xdg-mime settings for the file type and open them in unexpected apps, printer does not work… But those are just bugs, and they need to get reported and fixed.