My system is Dx12 as well and runs S4 just fine; Direct X is backwards compatible somewhat, so running 11 from 12 should not be an issue.
If you go into the Dx Diag Tool and look at the Display Tab for the card you use to run the game and look at the right side under Drivers you'll see 'Feature Levels' under 'Direct3D DDI 12' and it will show you what versions of DirectX you can run. The lowest version of DirectX that my Dx12 system can run is Dx 9_1. *For reference I'm also on a Predator but a PH315-54-74FG system with a few tweaks/not stock.
You might want to look deeper into your CPU as it's an i9; there have been numerous reports of players having issues trying to play with i9 processors. Do a search for "sims4 i9 problems" to get started.
I'm not saying in any way that you can't run S4 on your new system, but from what I understand there are special measures that those with that CPU need to take in order to play.