After some tweaking of settings, games runs fine. I shouldn't HAVE to do those things, but it's doing fine now
For reference, 3700x, rtx 2070s. Game heavily gpu bound. 50-60fps, no lag, no stutter , no whatever, honestly I never noticed losing a couple of fps, and that's just in crowded cities/areas, in other place it'll go higher.
What I did :
update drivers
installed free dlss mod from nexus
most setting on medium, render scale 50%, shadows on low
After doing this, everything has been 100% fine and never had any other issues. Before, I sometimes had slideshow in new Atlantis, heavy stutter, occasionnal massive fps drops. But these 3 things have 100% resolved my issues entirely