You have a creative cloud subscription. But you are trying to install the standalone version of Lightroom. It's only the standalone version that requires a serial number. It cannot be activated with a creative cloud subscription. In that list of apps in the creative cloud application manager, if you scroll down you should find Lightroom available for you to install. It will have to be installed from the creative cloud application manager. Then everything is managed with your Adobe ID and password. They are used to validate that your subscription is paid current. According to that list, you haven't even installed Photoshop yet. Both Photoshop and Lightroom need to be installed from that application manager dialogue.
Ok I installed Photoshop itself as well, although I will never use it.
My problem is, Lightroom will not launch from the creative cloud even though it says its installed and up to date.
The creative cloud application manager is apparently seeing The standalone installation and is reporting that it is up to date. But you cannot activate Lightroom from the creative cloud with a serial number because there isn't one. You'll have to install Lightroom. Then you might have to quit the application manager and sign in again before Lightroom is listed as available for installation. Then, install from the creative cloud application manager and you should be good to go.
Incidentally, I still have Photoshop CS6 installed on my computer. It isn't part of the creative cloud program. But the application manager reports it as installed and up-to-date. When I first installed the creative cloud, Lightroom was listed as up to date even though it was the standalone version. The only way you are going to resolve this problem is to uninstall Lightroom and then install it from the creative cloud application manager.
Yup. That worked. Thanks mate!
I uninstalled LR from the control panel. Exited Adobe CC. Restarted adobe CC and it had the option available to install from there.