All that was said here, plus sometimes they don’t work. I’ve reported a bug where the kdenlive flatpak version doesn’t render titles or fades - and that’s on Debian Testing, Arch, and Asahi Fedora. Native version works perfectly, but forces me to download an untidy amount of KDE stuff on my gnome installs ; flatpak would’ve been a cool solution to that.
I am yet to report another where Ardour nukes pipewire, at least on Asahi, but on Arch it was misbehaving also. Native, distro-provided version works perfectly.
I don’t trust flatpak because no one single publisher can test every possible config, and I’m afraid distros become “lazy” and stop packaging native versions of stuff since it’s a lot of work.