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??"
I'm a firm believer that regardless of operating system that a warning message saying that installing something could cause harm to your device definitely makes people think twice about installation if they're not tech savvy (AKA know more than the bare minimum anymore). It's definitely intentional that the large companies responsible scare you away from doing the things you want because they want you locked into doing things the way they want.