I’ve compiled libwebp to WebAssembly and made a web page to use it: https://qip.dev/webp-to-png

You can also run the same wasm on the command line:

  npx @qip.dev/qipx qip.dev run \
    image/webp/webp-to-ktx2-r8g8b8a8-srgb.wasm \
    image/ktx2/ktx2-r8g8b8a8-or-b8g8r8a8-srgb-to-png.wasm \
    < input.webp > output.png