The message I mentioned showed up after adding the repo ("dnf copr enable
@kdesig/plasma-5-unstable") and clicking on Software Updates / Check for Updates in
System Tray. In response, 56 packages (5.9.3 related) were reported as available for
upgrade, so I thought a "dnf update" was not necessary.
I repeated the process removing the repo with Apper, re-adding it through CLI followed by
"dnf update". It did work - packages were downloaded and upgraded as expected!
Thanks Rex for making this available in copr and helping me with the upgrade process! I
will report anything I may find.