So I just got this off of GOG to play the original version of the game. Unfortunately for whatever reason the game has graphical issues, the cursor is in a green box as well as a fair amount of the assets in the menu and in the overworld. Can't find a fix even after turning on Software Transparent BLT which allegedly solves the issue, but it doesn't. Thoughts? This issue is preventing me from enjoying the game.

Have you tried turning on any other options in the graphics settings? Apart from that, if you have Nvidia card there's a fix for some graphics issues, you can give it a try:

https://www.mediafire.com/file/o2zx0c2qb23jiis/nvidia_fix.zip/file

One more thing that comes to my mind that could help is dgVoodoo2, that is able to translate DirectX game into Direct3D and acts as a wrapper:

http://dege.freeweb.hu/dgVoodoo2/dgVoodoo2/

Here's a post describing how to set up dgVoodo2 with the original Baldur's Gate:

https://www.reddit.com/r/baldursgate/comments/lx6d1k/how_to_run_original_baldurs_gate_and_other_old_ie/

and prayers.

PS the reasons are quite clear tbh