This build needs hardware-accelerated WebGL (OpenGL ES in the browser). Embedded or sandboxed views often report Sandboxed = yes / GL_RENDERER = Disabled and cannot create a context.
Fix: Open this same URL in a normal Chrome, Edge, or Firefox window (not the Simple Browser / preview panel in some editors).
From a terminal:
cd build-wasm && python3 -m http.server 8000
Then in the OS browser go to http://localhost:8000/magicor.html