Update Catalina

I have an older system with an early version of Catalina. I'd need to update it to a late version even 10.15.7. I go to Software Update and am offered Big Sur and nothing else, no additional software versions. I try the App Store. Search for macOS Catalina doesn't offer a downloadable version. When did this happen? I used to be able to get both Catalina and Mojave downloads. Surely these are available somewhere. I find Downloads and get this

Really? No results for Catalina? You're kidding.

This is pretty embarrassingly pathetic. I'm sure I'll find it somewhere, but this is really bad.