James, I do not know if your solution works for all, but current state of that in the unstable branch of updates matches your solution:
~/Desktop ❯ pamac search manjaro-kde-settings -i
manjaro-kde-settings 20211211-1 community
Manjaro Linux KDE settings
~/Desktop ❯
have no...-19.0 and have simple-named one installed.
Hm, it looks like you have old unused package, cause the ISO image file of unstable branch built on about Aug-2021 was never included the package ...-19.0:
details
~/Desktop ❯ grep "manjaro-kde-settings" /var/log/pacman.log | tail -n 10
[2021-08-23T17:36:23+0300] [ALPM] reinstalled manjaro-kde-settings (20210813-2)
[2021-11-17T10:58:28+0300] [ALPM] reinstalled manjaro-kde-settings (20210813-2)
[2021-11-17T11:53:19+0300] [ALPM] reinstalled manjaro-kde-settings (20210813-2)
[2021-11-17T12:06:36+0300] [ALPM] reinstalled manjaro-kde-settings (20210813-2)
[2021-11-29T02:42:05+0300] [ALPM] upgraded manjaro-kde-settings (20210813-2 -> 20211128-1)
[2021-11-30T17:52:59+0300] [ALPM] upgraded manjaro-kde-settings (20211128-1 -> 20211130-1)
[2021-12-04T19:12:05+0300] [ALPM] upgraded manjaro-kde-settings (20211130-1 -> 20211204-1)
[2021-12-05T22:40:15+0300] [ALPM] upgraded manjaro-kde-settings (20211204-1 -> 20211205-2)
[2021-12-10T09:00:07+0300] [ALPM] upgraded manjaro-kde-settings (20211205-2 -> 20211209-1)
[2021-12-11T15:40:10+0300] [ALPM] upgraded manjaro-kde-settings (20211209-1 -> 20211211-1)
~/Desktop ❯
also initial package list state (Is it safe to delete desktopfs-pkgs.txt and rootfs-pkgs.txt?)
~/Desktop ❯ grep "manjaro-kde" /desktopfs-pkgs.txt
manjaro-kde-settings 20210813-2
~/Desktop ❯