Imagine your friend that does not know anything about linux, don't you think this would make them not install the firefox flatpak and potentially think that linux is unsafe?
I ask this because I believe we must be careful and make small changes to welcome new users in the future, we have to make them as much comfortable as possible when experimenting with a new O.S
I believe this warning could have a less alarming design, saying something like "This app can use elevated permissions. What does this mean?" with the "What does this mean?" text as a clickable URL that shows the user that this may cause security risks. I mean, is kind of a contradiction to have "verified" on the app and a red warning saying "Potentially unsafe", the user will think "well, should I trust this or not??"
Fedora has pretty good SELinux configured out of the box, and isn't focused on opsec. It's just sane defaults and proper limitations to access. It also switched to Walyand-by-default this release, completely removing X11 from the default packages, which mitigates many of the "app spying on other app" scenarios that a previous user in the thread was talking about. That's not to say that Fedora is the pinnacle of Linux security or anything, but it comes with pretty good defaults for the average user. You'd have to get into kernel hardening and deep into SELinux to do better as an end user, which is not something that most users are inclined to spend time or energy on.