m15 r4, keeps booting up after shutdown

I have replaced 1TB SSD nvme drive with a 2TB one (WD Blue SN570: https://www.westerndigital.com/en-ca/products/internal-drives/wd-blue-sn570-nvme-ssd#WDS200T3B0C) couple of weeks ago. Followed procedure in the Service Manual (also, not my first rodeo) and once I powered on the laptop, it booted into BIOS saying that date and time needs to be set, which I expected because I disconnected the battery while replacing nvme drive, as is specified in the Service Manual.

Once the date/time has been set, laptop booted up with no issues, I formatted the 2TB drive, copied some stuff to it and went on to shut down the laptop. It did shut down, as usual, but then about 4-5 seconds after it shut down, it powered on and booted up again. I shut it down once more from OS, as I always do, it powered off and again, after 4-5 seconds it powered on and booted up.

The only way to shut it down is to hold down power button as soon as it starts booting on its own, until it powers off.

I tried shutting it down both with power supply connected and running on battery only, same thing. I also closed the lid after I did shut down from OS, and laptop just powers on with the lid closed and all.

I then performed the "Drain residual flea power (perform hard reset)" procedure from Service Manual, which resulted in laptop booting up into BIOS screen asking me to set date/time, which I did, proceeded to boot up, and again, after shutdown from OS, it powers up on its own again. I also checked BIOS settings after I did the "hard reset" procedure, and none of the few changes I had in there were reset, so I'm not 100% sure that the "hard reset" procedure from Service Manual actually does anything other than clearing RTC (and draining power capacitors).

After laptop powers up and boots on its own, dmidecode tool says "Wake-up Type: Power Switch", so as far as the OS is concerned, the system started because power switch was pressed, which definitely did not happen.

BIOS is v1.4.0 and I have no plans of updating it because I did that on another Alienware (work laptop) and lost DP output on USB-C port so now I can only use one external monitor on that one.

I can't find anything on Internet, almost all power/boot issues are about laptop not booting up, whereas my issue is kind of opposite: it boots up on its own.

I would appreciate any thoughts on what may be causing this and/or what I could try to mitigate the issue.