While I know that you're not affiliated with Proton or rather Proton-GE, I still think this is the correct place to report this.
If it's not, I'm sorry for wasting your time and this can be closed.

The game has quite a few less fps on newer versions (9-15+) of Proton-GE, compared to older versions (9-10-):
I noticed that the biggest drop happens if I move the mouse in-game, if I unfocus the window the fps are at its peak and the highest.
You can also go into cursor mode and this increases fps the same as unfocused on GE-Proton9-7, but not on 9-15+.

Since I don't have windows anymore, I can't test and tell if the behavior of decreased performance while the camera is moving is normal or not. I will add this information as soon as I can get a friend to test this.

Also, this is unrelated and from my research the fault of NVIDIA:
The RAM usage is higher than on Windows by 2-3GB (Windows ~3GB, Linux ~5-6GB).
I just want someone to confirm to me that it's an NVIDIA issue, as the results from my searches were fairly...unpromising.

If I phrased something poorly and you have trouble understanding, please just ask and I'll try to rephrase. English is not my native language.

GE-Proton9-23:

• default = 135 // 150 // 160 // 220
  (camera movement // no camera movement // in cursor mode // unfocused)

GE-Proton9-7:

• default = 170 // 220
  (camera movement // no camera movement, cursor mode and unfocused are the same here)

Software information

Game: Black Desert
Launch Options: DXVK_CONFIG="dxgi.syncInterval=0" PROTON_ENABLE_NGX_UPDATER=1 PROTON_HIDE_NVIDIA_GPU=0 gamemoderun %command%
Settings:

• Borderless Windowed
• 1440p
• High Textures
• Slightly High Graphics
• SSAO on, all else off

System information

• GPU: RTX 4090
• Driver: 565 as well as 570
• Wine version: I don't know, sorry
• DXVK version: I don't know, sorry

Apitrace file(s)

• Opted to not do this, as I don't know how with Steam/Proton
• If needed I can provide it, but I might need steps on how to do it

Log files

Please attach Proton or Wine logs as a text file:

• Logs are me entering the game, waiting for a bit for things to load, moving the camera/mouse, holding the camera still and then unfocusing the game.
• steam-582660-GE97.log
• steam-582660-GE923.log