There are dual-fuel generators, Ecoflow has a propane+gasoline option [1]. The problem with a pure propane setup is that propane doesn't really want to get gaseous if it's too cold outside - just like your cigarette lighter that you need to warm in your pants pocket before it can actually light a fire.
Diesel plus <any other kind of fuel> isn't available on cheap residential units I'm aware of, particularly as the ignition and fuel injection mechanisms are much more complex than a gasoline/propane mechanism.