How to download Mojave now that Catalina is available?
Open the link in Safari so that it finds the Mac App Store to open the application.

https://support.apple.com/en-us/HT210190

If you have failures after getting the Mac App Store to receive the link or the installer is too small or doesn’t work, this post is amazing and can help with different issues specific to machines and OS versions.

How can I download an older version of OS X/macOS?