I moved the app with “Preinstallled Apps” as you and others discribed, restarted the fp5. I also tried to install again from Fdroid but nothing works. The fossify-messenger doesn’t appear - nowhere.
I am trying hard to break Preinstalled Apps (get it in the confused state where “Preinstalled Apps” shows it installed but it isn’t installed) and just can’t do it! I guess I keep trying to see if I can break it…