How to get old versions of macOS
The other day I was formatting an old Mac and I had to download the macOS Catalina from the internet. If you go to the App Store on your Mac the only available version is the most recently version which today is Big Sur.
I quickly found this page with all the link that will open on your Mac and start downloading the version you have chosen within the System Preferences -> Software Update.
But here is the catch the link on the page above will only work if you use Safari. It took me multiple trial and many Googling laters I had an enlightening moment and decided to use Safari. Voila, it worked link a charm.