Confirm your browser actually supports WebGPU
WebGPU is the new GPU API for the browser — different from the older WebGL. Web Stable Diffusion will silently fall back to a sad error message if WebGPU isn't enabled. Check first.
webgpureport.org says WebGPU is not enabled.
Open chrome://flags, search for 'WebGPU', set 'Unsafe WebGPU' or 'WebGPU Developer Features' to Enabled, and restart the browser. On Linux you may also need to enable Vulkan.