The current version of PulseEffects on FlatHub is the 4x maintenance version. I seen comments on various internet corners of people complaining about wanting 5x PulseEffects. Some may be unaware that it requires Pipewire, and will not work on PulseAudio systems. I think Flathub should package a separate version of PulseEffects with (Pirewire) in parenthesis and explain that it will only work on distros with Pirewire.
Flatpak has the ability to do these things, where as a traditional package manager would struggle on using two versions of the same app.