In 2015 I bought Lightroom 6, I still have the license key. I have a new laptop, so I want to install Lightroom again. I deactivated my account on my old laptop and installed a trial Lightroom through the creative cloud app. Now it seems that I need to choose a payment plan to activate it, but I just want to use my old license again, I don't want to have to pay monthly to use this program. So, how do I do that?
Your license key is for Lightroom 6. The trial version you have installed is for the new plan which is subscription based, and it doesn't use any license key. You subscribe with an Adobe ID and password that is activated with the subscription payment. You cannot activate the current version of Lightroom with a license key.
Lightroom 6 is out of date and unsupported by Adobe. You can try contacting them and explain your dilemma and ask them for a link for the installer. Click on the little circle in the lower right hand corner on the webpage on the link I am providing.