Hi! I'm the Chrome dev that's been working on WebGPU's Android support. As jsheard said the older exynos devices will work because they're Mali-based. The newer RDNA3-based devices aren't enabled by default simply because our team hasn't been able to sufficiently test on them yet. Same goes for Tegra or PowerVR GPUs.
It's entirely a question of spending the time to ensure they're performing as expected (and probably implementing a few workarounds) and not a comment on the quality of the GPUs themselves.
That said, we know that these GPUs are in an increasing number of flagship devices, which makes them a higher priority for official support in future releases.
WebGPU is not based on Metal. Apple did an experiment several years back in Safari which they called WebGPU at the time. It was effectively a thin wrapper around Metal, and so that's caused some confusion, but the actual W3C WebGPU spec has nothing in common with that experiment. It's a carefully selected set of features that are feasible to run effectively on Vulkan, Metal, and D3D12 and structured to feel like a web-native API.
It's entirely a question of spending the time to ensure they're performing as expected (and probably implementing a few workarounds) and not a comment on the quality of the GPUs themselves.
That said, we know that these GPUs are in an increasing number of flagship devices, which makes them a higher priority for official support in future releases.