Comment 3 for bug 1881374

This is a known limitation of the current implementation. Previously, it was not possible to remove already installed packages using GNOME Software (because they are not present in system AppStream metadata). There used to be an "Install" button always displayed for local packages, but it actually did not work if the package was already installed. So, an actual local package detection code that displays a "Remove" button if the local package is already installed was added, however the "Update" part code/button was not added because there was not enough capacity/time to properly implement this, see this comment from Matthias Clasen: https://gitlab.gnome.org/GNOME/gnome-software/-/issues/965#note_789500