I've also been on immutable Fedora for a while, and the biggest complaint I have is that I need to reboot after removing software from the base system. Otherwise I quite like Flatpak for the ability to set granular permissions per app. KDE even has Flatseal built into the settings app now, which is super nice.
Kinoite user here, the majority of my desktop apps are in flatpaks already. I have a couple of things in toolbox/distrobox containers
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