To answer my own question: in Epic Games launcher: click on your avatar picture in the upper right corner select "Settings" in settings, scroll all the way down to "Manage Games" there is the option to add launch parameters. See screenshot below (German)
I find no advantages of using the -dx12 option for TSW3 on my system (i7-12700K, 3070ti). If anybody has different experiences, I am curious to hear about it.
I have 3050, on 1920*1080. Suffer from stutter. After long test. These are two work badly. Sky quality: Low VSync: Off After setting, it became smoother, but still stutter sometimes. Other methods have no obvious effect.
I find a huge difference on my PC, 5600X + Rx480. The stuttering is unbearable without DX12 enabled. On Battlefield, it's the other way around, but then again, my FPS are in the hundreds in that game so it doesn't matter that much.