DX12 did not use to work for me, on my RTX3080.
Now using a 4090 and DX12 is smoother. You notice it when taking off, arriving, all the time. It supposedly uses more VRAM, I have not checked that, but that is no problem for a 4090. If it puts that VRAM to good use, I am all for it.
I have had some artefacts with addons, so I removed those. For example the city of Antwerp on flightsim.to glitches. That could be because I also have Rex Accuseason. Both Rex and the Antwerp addon, add a lot of geometry to the scene, and sometimes you see glitches of the original geometry. With the Antwerp addon removed, the glitches are gone. And the default city is pretty good anyway.