where is mac OS catalina?

Open in Safari…

https://apps.apple.com/us/app/macos-catalina/id1466841314?mt=12

I have tried going to the link above to download Catalina. But all I get is a blank screen? I am using Safari 12.1.2. I had updated to Big Sur from Sierra and it has made my Mac mini (2014) unusable. Worked for a while but got progressively worst to unusable. Any help would be great.