This installs the plug-in that creates papat galleries from Lightroom Classic and brings your client's selection back.
It is installed for your user account only — no administrator password is needed:
~/Library/Application Support/Adobe/Lightroom/Modules/papat.lrplugin
If papat is already installed, the old copy is moved to
~/Library/Application Support/Adobe/Lightroom/papat-lightroom-backups/ first.