I am very happy that I have found this threat.
I bought an iPhone 12 Pro 512GB (white) with serial F2xxxxxxxxxx last week at German Amazon.
On first start everything worked OK. I turned it off to to do restore later on. At the second power on I have seen this strange behaviour. I restarted the iPhone with a "reset" - same strange behaviour.
I did a "recover" and a "DFU recover" with iOS 14.3 and the issues persists.
Today I called the German Apple Support. The support agent searched the knowledge database for this "logo flash issue" -> no hit.
The agent did a remote diagnostic and the diagnostic indicated -> "no issue found"
Therefore that "no issue were found" the agent told me, that a swap of the device isn't possible - I can just send the device in for repair. :-(
The agent recommended that I return the iPhone to Amazon for a refund and buy another one some weeks later...
Currently Amazon is sold-out therefore I have to wait anyway.
I hope that Apple will find the root cause soon!