Can MDS be used to downgrade to Mojave?

I have used MDS to reinstall Catalina on a 2018 MBP, but this same process does not work to downgrade to Mojave (install Mojave dmg on a machine running Catalina). Is it supposed to work? Do I need to do something different to get it to work?

Thank you. This MDS is a great time saver!

you need to boot from Mojave (or earlier) to install Mojave. This is usually done by booting to an older internet recovery partition (command-option-shift-R).