Ok, I think I know the problem. Go to finder and press command + shift + g. You want to type your username, so my username is jd, so I would type:
Inside Library create a folder called Frameworks. Next go to https://www.libsdl.org/download-2.0.php and download SDL2-2.0.7.dmg. Take the SDL2.framework file and put it into the Frameworks folder. I think that should work.
Don't put anything in your base. All you should have is KotF 2.1 SP, KotF 2.1 MP, and the KotF folder.