Unfortunately it just doesn't seem to succeed. I've retried all three methods ("install" from file manager, "pkcon install-local" and "store-client install"). "Install" from file manager as well as the pkcon method always claims success, but no app icon appears. Installing with executing store-client install in terminal acts a bit weird to me, but I don't know if it is normal... If I haven't fired up Store app after reboot, I get Account credentials need update but updating the credentials / login info via the GUI just doesn't seem to do any good, and I need to kill the store-client process. After that "store-client install" fails with Service name is already in use: "com.jolla.jollastore".

I'll give up with this for now unless someone is able to suggest something. At least I've been able to install Warehouse manually and the Store client works ok with the official content...