Only the latest two versions of Creative Cloud are supported and available for download using the Creative Cloud app, so that would be CC2019 and CC2020. May I know why do you want to use an old version when you already are paying and eligible to use the latest version at no extra cost. Is it some plugin that you use or something else?
On the Creative Cloud there are the CC2017, CC2019 and CC2020 versions. Inexplicably, only the CC2018 version is missing. Maybe it was eliminated because it had problems. I need to use CC2018 because a customer asked me to use this version exclusively for internal reasons. Thanks anyway for your reply.
You see CC2017 because you must have that installed on your machine. If it's already installed then Creative Cloud shows it but it will not show/allow any version except the last two for new downloads. The site mentioned by John does have the installer for CC2018, I was able to get a download, what issues are you facing? Also, the download links on this site are genuine links pointing to Adobe servers, if these links don't work then you can be sure that there is no download for these files available now. Don't trust if someone provides you with an installer, more often then not it is laced with malwares and viruses.