Catalina won't download
I am running Mojave on my MacBook Pro 2017. When I try to download Catalina, a message says my system is up to date.
MacBook Pro 15", macOS 10.14
No, you can do it. The Terminal program is in the Applications/Utilities folder. Double click it to open. Copy then paste the command I posted into the Terminal window. Press Return. It will ask for your user password, type it in then hit Return. Then you can quit the Terminal. Then reopen System Preferences > Software Update.
If you have any problem, ask.