Well, the issue is that Discover is the default updater and packager on the PinePhone (on the current Beta Edition, even out of factory) and is just too broken to be useful (see Discover system updates still very unreliable). As an experienced GNU/Linux user, I can fix the issues it caused for me, but even for me, it is just too broken to be useful and I have basically switched to pacman on the CLI. (I basically had to always do that after a Discover system upgrade anyway, so I figured I might as well use the CLI to begin with and avoid the painful to recover breakage.)
I have been wanting to try out pamac-gtk with pamac-mobile-integration for a while, now that GTK is no longer semi-broken on Plasma Mobile (see the fixed bug 452967 – kwin_wayland: touch input does not reach GTK or Chromium popup menus (subsurfaces)), but have not yet. But what is sure is that Discover is just not a workable solution as long as nobody feels responsible for upstream maintenance of the PackageKit alpm backend. (Hint: PackageKit upstream considers it the distribution’s job to maintain its respective PackageKit backend in upstream PackageKit, so someone from Arch, from Manjaro, or from any other Arch derivative needs to take care of it or it will remain broken forever. Filing it off as an upstream issue is not going to work. Either you find someone who does the work, or you need to stop shipping a PackageKit-based package manager by default.)