Desktop turns on automatically

I recently got a new 7010 tower (new as in 2023 launch, not the previous one).

Since the day one, whenever I turn on the main power switch on the wall, the desktop gets turned on automatically for 3-4 seconds, and then turns itself off. The OS does not start to load. After that, like normal, I have to turn on the system by pressing power button on the cabinet. Everything works normal/fine after that.

I was not sure why this was happening, so checked "power settings" in BIOS, and the option was set to stay turned off in case of power interruption. I looked at multiple sites/forums, and when I could not find an answer, I contacted Dell support. They took almost a week to understand the problem, and at the end, they said they would replace the PSU, and motherboard.

When the technician arrived, he asked me the issue, I told him, and he was like "in some systems this is a feature... I think". I said I spent almost a week explaining the online tech support the issue, ran several tests, they told me to make a clean install of Windows, and stuff. He was kind of confused, but he was sure there was no issue with the system. But he replaced the parts.

The system behaved exactly like before. The technician said "see... I told you there was no problem with system. The online (Dell) tech people don't know what they are doing". Then I realised/dawned on me, the tech support couldn't even understand my issue for the first two days. One guy even thought that I was regularly pulling out the power cable from cabinet, otherwise it would not power off. I am not sure where did he get that from. Another guy thought the system was stuck in a loop of restart(s) (it took me almost an hour to explain the issue to the second guy).

I apologise, I drifted off the point. My question is: is this a feature/function, or an issue? Is this some sort of POST process? or is there some other issue with hardware?

Currently, the unchanged hardware is SSD, HDD, ODD, external wifi's card, RAM, and processor. I have already tested the system by removing the wifi card, still the same issue. Should I also try removing other components, and in RAM's case, should I test the system with different RAM stick? Or is the turning on and off automatically actually some sort of function?

Thanks a lot in advance.