[Review] Is it a Bug or Feature of 'Big Sur'?

Recently I've downloaded the latest macOS 'Big Sur'. While downloading macOS, I'm also watching video on YouTube (Catalina macOS). As soon as it's downloaded I was curious to install it.  

I've started the installation and Catalina MacOS closed all the apps which were running.

See more in the video what I've found 😀😀😀