[2020] Unable to load saves

Your friend has a pre-order edition of the game which is where that DLC comes from, it is a pre-order bonus only. Royal Edition comes with a lot of stuff, but only pre-order bonuses if bought before release date.

Potentially you and your friend could set up Steam Family Sharing so you can load with that DLC enabled, borrowed from his library. I can't think of another way around this, I'm sorry!