PhotoQt is available on Flathub. If you don't have Flatpak installed yet, please refer to the official installation instruction by Flatpak.
With Flatpak installed on your system, you first need to add Flathub as a remote (if not already added):
$ flatpak remote-add flathub https://flathub.org/repo/flathub.flatpakrepo
Following this, you can install PhotoQt by running:
$ flatpak install flathub org.photoqt.PhotoQt
After the above has completed successfully, you can run PhotoQt using this command:
$ flatpak run org.photoqt.PhotoQt
Flatpaks integrate very well in various window managers, like KDE or Gnome. They should show up next to all other installed apps and can be launched and used like any other application.