Like you said yourself, creative cloud has a password. So if you log out in the creative cloud app, then Lightroom won't show your library until you have logged in again first (although it may still show the local cache, in which case there is nothing you can do about that). There are no options to password protect something else like that local cache, or part of your library like one album.
You log off by opening the creative cloud app clicking on the top right icon that looks like a nose and hit sign out.
Also, you should password protect the account that you use to log onto your windows or Mac machine and make it always ask for a password when waking from sleep and don't share the account password. Just make separate accounts for other users on the machine if you share the computer. This is another layer of protection that everybody should use anyway and also would make it so you don't have to log out of creative cloud.