If you read the FS2020 forums the developers are working on the DX12 and will be about soon, but they have also stated anyone expecting performance boosts not to expect them as DX12 will not help in that department but will add ray tracing and some more DX12 features but no performance boost to frame rates, so basically I read that to mean it will be prettier to look at and probably worse performance in DX12 mode. FSX did same thing too in past with it's broken DX10 "update" that actually made things worse and most people stuck to DX9 on it even to this day.
The FS2020 forums the devs there are stating a lot of things if you go read it and honestly there is a lot broken is FS2020 that needs fixing before the graphics updates and DX12, the planes have a lot of broken systems and other issues that didn't exist in FSX and previous MS flight sims. Still a lot of work needs to be done on it and I think only the true flight sim users have noticed the real issues with it, a lot of people are just using it to fly around and enjoy the scenery and not realising there are many broken things in it to make it a true flight simulator. Anyways I hope they get all the important issues fixed as so far anyone that uses the flight systems correctly will realise all the faults on the planes.