I think I've found the solution.
I think there's something wrong with in-game V-Sync settings. After disabling V-Sync from NVIDIA App or NVIDIA Control Panel, the game runs smoothly, and it's noticeable even in the game menu.
Do steps:
Right-click on NVIDIA icon in the Windows system tray -> NVIDIA control panel -> 3D Settings -> Manage 3D settings -> Program settings tab, then add "bf6.exe" to the list of programs, then turn V-Sync OFF for "bf6.exe".
You can also set Low Latency Mode to Ultra and set Power Management to Maximum performance.
Click "Apply", and launch the game.
From my feeling, disabling V-Sync OFF is crucial. The other settings are just additional.
I apologize if I made any mistakes in the menu names. I've set a different language on my system.
I think the same can be done in the NVIDIA application, which has a more user-friendly interface.
Now I think the game is worth the price, as I was really frustrated before.
I hope this helps.