I (hopefully) installed the plugin correctly on KI-Cad 6.0 by cloning it as described in

• /home/my-folder/.var/app/org.kicad.KiCad/data/kicad/6.0/scripting/pluginskicad-jlcpcb-tools/
• /home/my-folder/.local/share/kicad/6.0/plugins/kicad-jlcpcb-tools/

I tried flatpak and installed via rpm on Fedora 35/Gnome 41.2 and little earlier versions, but don't see any additional icons/buttons which could be used.