But this gets to the mindset that bugs me about Flatpak, the magical thinking that regressions don't happen. It's why Alice can't downgrade a system flatpak because it might introduce a vulnerability she uses to attack Bob, but it's absolutely fine if she upgrades to introduce that vulnerability.
Only when the version you want to downgrade to happens to be within the last 10 versions! Why 10? Beats me!
Case in point: the flatpak package for the Element messaging client seems to be the preferred installation method for non-debian distros. But for many users, encrypted message search is broken! [1] [2] Some users claim that downgrading can fix the issue, but the flatpak has been updated too many times now for any user to downgrade to an old enough version - tough luck!
[1] https://github.com/vector-im/element-web/issues?q=is%3Aissue... [2] https://github.com/flathub/im.riot.Riot/issues?q=is%3Aissue+...