Issue downgrading MacOS Catalina to Mojave using bootable install on 16 inch MacBook Pro
Downgrading MacBook Pro 16” to Mojave

The 16 inch MacBook Pro will not install Mojave. For those that are new versions of older gear like Mac Mini and iMacs, the drivers are likely good enough in Mojave so you can try using safari to download. There’s some good discussions on that below:

How to download Mojave now that Catalina is available?
How can I download an older version of OS X/macOS?
Mac OS X downloads do not begin, other app store downloads normal