Can i use CC 2019 as a downgrade right of CC 2020

You cannot "purchase" CC, so I assume you mean you have a subscription. (If you actually DO have a purchase, please give us a link so we can give you correct info).

CC gives you the right to run older versions but not the ability; Adobe do not block these old versions, but the Creative Cloud app only offers the current version and the one previous version. If you have an install and kept it, that's fine.

Hi @Chirag5C72,

The short answer is yes. However do note that Adobe officially supports only the last two versions of the CC apps and you purchase the subscription to CC not for a particular version. This means that officially Adobe wants you to use just the two latest versions of the software and that is all you get to download from official sources(CC Desktop App). However, if you have an installer for an older version like CC2019 or CC2017 or if you already have these installed and want to use them then you can use them, your subscription will treat it as a valid installtion

-Manan