Hi, sorry for the problem you're having. I have an HD 7970 and have had maybe a similar issue in other games. I've had some success by using Rivatuner Statistics Server (RTSS) to cap the frame rate at 60 fps. If you do try to go this route (not hard by the way, but does require installing another program) you'll need to add the Baldur's Gate 3 .exe file to RTSS's app list. This file is located in your Steam folder like this:
...\Steam\steamapps\common\Baldurs Gate 3\bin\bg3_dx11.exe
Then, also in RTSS, when you select bg3_dx11.exe from the app list, and set the "Framerate limit" to whatever you want, 60 ideally but you might need to go lower if your computer's struggling. To check that RTSS is actually controlling your FPS in game, try setting the limit to something like 5 and see if the game becomes all choppy.
Like I said, this has worked for me in other games to eliminate a weird tearing issue. Worth a shot. Also, make sure to play with various windowed/fullscreen modes and V-Sync if you haven't already.
