1. You cannot flash it from macOS (as far as I know). The only software option I know is flashrom and using a clip CH341A.Flashed in Mac os.There was no sound signal.Only one LED was on and that was it.
2. Have you ever heard a chime when booting the RX470 card within your iMac12,2?
3. Do the fans start to spin when powering on the iMac with the card installed?
4. Have you ever been able to boot Linux or macOS or Windows while the card was installed?