Many problems with Big Sur, I want to go back to Catalina.

I upgraded my 2015 MacBook Pro from Catalina to Big Sur about a month ago. Problems with waking from sleep; either slow wake up or spinning beach ball when trying to wake. I don't like the look of it either, much prefer the look of Catalina.

I've checked some sites that advise how to go back, but they all say to download a copy of Catalina. But everywhere I've looked for Catalina, the sites just redirect to Big Sur. What do I do?