Install SDL2

The first step is to get all files required into your system.

Download SDL2 by picking the .dmg one from the release list:
https://github.com/libsdl-org/SDL/releases

Execute the SDL2 file (will be named something similar to SDL2-2.30.10.dmg) and a window will open with a few files and an SDL2.framework folder.

Open Finder, click Go then Go to folder... and type /Library/Frameworks which will open the contents of that folder. Drag SDL2.framework to /Library/Frameworks

now try and run WebTV on MAME again.
(fn f1 to power on)