What is OBJ?
Wavefront OBJ is the closest thing 3D has to plain text: a list of vertices, one per line, then faces referencing them by index. It has been readable in every 3D tool since 1990, which is why it survives as the format people fall back on when nothing else will open.
What is GLB?
GLB is glTF packed into a single binary file - geometry, materials, textures and a node hierarchy in one blob. It is the format the web actually uses for 3D, and the one most viewers, AR tools and game engines want.