I've been facing this issue ever since launch. I played with Vulkan just fine in pre-release, with my old and worse build (and it ran better than DX11)

My old build was:

GTX 970
i5 4690
2x4 ddr3 @ 1666mhz Hyper X
WD 7200 RPM 500 GB HDD

I managed to get to act 3 with a slow ass HDD until I kept dropping to 15-20 fps, so I kinda quit the game until I had an upgrade. I finally did manage to get something better:

Intel Xeon E5 2680 V4
4x8 DDR4 @2666mhz (capped to 2400 due to cpu max limits), quad channel
Storage: Huadisk Nvme m2 3.0 SSD, 500 GB, 3500R, 2400W
Still packing the GTX 970

I thought it could be anything related to a mix of low ram, HDD, old 4/4 cpu but no! I tried setting up the game in Vulkan and the same happened. I really dunno what to do and DX11 does not take advantages from my CPU's extra cores (of course, to the limit of the gaming industry, I know the cap is at 8 cores and most games at 6).

Pre release gameplay: https://www.mediafire.com/file/gsq4cggfvu8fgi8/Baldur%2527s_Gate_3_2023.07.30_-_15.22.01.01.mp4/file

[Linked Image from i.imgur.com]