ASUS Strix X670E-F killed my 7600X during BIOS update

On 13th October (I know, the worst possible date I could pick for a BIOS update) I was updating from the BIOS, from 1303 to 1709. After 5s PC restarted itself and it hanged on orange DRAM LED. I also tried it in ASRock X670E Pro RS, there it was red CPU and DRAM light.
Since then I also sent the CPU and ASUS mobo to repair center and they said the CPU is dead.

My SoC and VDDIO were at 1.30/1.25V before update, but right before update I loaded system defaults, so it was 1.40/1.40V for a brief time. But I had it at 1.40/1.40V for the first 7 months as I only read about X3D CPUs dying end of April 2023.
So voltages couldn't be it, CPU is also like new on the underside.

Is this a common thing (I mean 1 in a 1000, of course it is not very common) or a one in a million?

How to avoid this next time? Since then I update BIOS from the back USB labeled BIOS (BIOS Flashback). If you don't even need CPU and RAM to flash it, I would say this method is very close to 100% safe. Possibly even 100%, unless this method can also kill a CPU.
But from BIOS it is more like 90% safe as I didn't have problems before and I flashed at least 15 BIOSes (including all my previous mobos), but now I had the worst possible outcome.

The only possible way to avoid this is set the voltages yourself & watch them over all loads including no loads.
boards killing cpus right now isn't an uncommon thing, as of a two months ago this was a known issue.