Is “Use Full GNSS Raw Measurements ” in the Android Developer options? Could you share a screenshot of this?

Don’t pay attention to the “H/V Acc” number in terms of accuracy — that’s just an estimate provided by the device OEM and may not be accurate itself. To measure true accuracy you’ll need to compare the calculated location values from the Mi 8 against a ground truth location provided by yourself. I hope to add a basic accuracy benchmarking feature to GPSTest in the near future, but in the meantime you can try an older app I developed GPS Benchmark (https://play.google.com/store/apps/details?id=com.gpsbenchmark.android).