Web serial for USB serial on android relies on an as yet unavailable system service that will be released in Android 17 and then only if your vendor enables it. For now it only works for Bluetooth emulated serial devices apparently. Chrome developer blog should have mentioned this really.
Chrome Beta 148.0.7778.4 is now available on Android through Google Play, adding Web Serial API support, SharedWorker on Android, and a broader set of Chrome 148 web-platform changes.
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