You say you have 'a lot of problems' but you only mention two.
FPS drops are not necessarily down to your hardware - they could be due to the game area that you are in.
If the black squares are always in the same place on your monitor then they nay be down to your monitor.
1. Update your graphics drivers.
2. If you are using DX11 then try switching to Vulkan.
3. Check what screen resolution you are using and change to 1080 x 1920 @60Hz if necessary.
4. Lower your settings in the options to low and then raise them one at a time until the problem(s) reappear.
5. Have a look on YT to see if there is a video or three about optimising your video card for gaming and or BG3.
