Going back to Mojave - Catalina is a disaster

So many things don't work with Catalina, wished we never upgraded. Lots of sheets we can't read even after having bought new Office 365.... unable to upload photos to websites. Loads of time waste. Terrible idea to upgrade.

What is the safest way of going back to Mojave?

Will Time Machine back ups work pre Catalina, I read somewhere that I need to have Mojave downloaded on a separate hard drive before going back? Or will reinstall from a Time Machine pre Catalina be enough.

Thanks in advance for any help!!