I would suggest you to uninstall Lightroom from the computer, and then install Lightroom from Creative Cloud.
How will I be able to install LR from CC without buying it again?
First uninstall Lightroom, and then install Creative Cloud from the following link: Download Adobe Creative Cloud apps | Free Adobe Creative Cloud trial
Once install Creative Cloud from the above link, you can go ahead and install lightroom from within Creative Cloud.
There will be no need of buying it again, as you will have to sign in to creative cloud from the email address that you had bought earlier.
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Your version of LR thinks it is running in standalone mode.
A simple log out and log in from the LR "help" menu may solve the problem.
If not, uninstall and re-install via the CC app may be your best bet.
if I uninstall standalone LR and reinstall CC, will I love my folder setup?
LOSE, not love. Of course I do hope I'll love it too
No, the catalog and all of the work you have done are user files and will not be affected by reinstalling. After you reinstall you should just be able to pick up where you left off.