Welcome to the club

The PL settings only deal with the maximums and how much power can be drawn and for how long, they don't affect idle power consumption.
I have an older i7 7500U 6 LAN port which draws 4 watts at idle with 3 active network connections, so anything more modern built on more efficient lithography should not be drawing what we typically see when sat at idle.
I think you are right, unlocked settings do not change how these types of board work with power management and C-States, I've certainly seen no differences. So we can only speculate at what is going on. These devices are cheap, and cheap for a reason. Often they cost little more or even sometimes less than the cost of the Intel SoC they house, so we have to be suspicious.
So what could be going on? Well, it could be the AMI BIOS isn't coming with full support for these newer CPUs, and it wouldn't surprise me if the AMI BIOS that arrives on these cheap appliances is unlicensed and outdated. Would Chinese manufacturers ship with an unlicenced out of date BIOS, you bet they would if they can get away with it! For example, Topton advertise the ability as an OEM to supply their PCs with cracked Windows software!
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Toptonpc
Building a motherboard with voltage regulation that can cope with sudden demands for power one millisecond, then dropping to next to nothing a few milliseconds later is expensive, it needs lots of testing and validation, extra components and good quality ones at that, have they just gone cheap on the voltage regulation then disabled power management options so the board remains stable?
The Intel SoCs? Why do we see the same SoCs flooding Aliexpress over the years? The N100 came from nowhere than is everywhere on Aliexpress, with no hardware seemingly able to use less than 12 watts when idle on a chip marketed by Intel for being ultra low power? Yet hardware from other vendors with an N100 can idle at a few watts, whether that is in branded laptops or single board computers from companies like Odroid.
For a long time it was flawed Celeron's in these types of devices being sold too cheap to be true, they never told customers it was because the CPUs were prone to failing over time due to a hardware flaw
Intel update on Celeron J1800, J1900, N2807, N2930. Did these type of appliances ever get to ship with fixed steppings of Celeron's or just used to off load bad batches of CPUs? So are Intel selling SoC's that maybe failed validation for low power use (i.e. they aren't stable in low power states) so no good for their target audience of laptops and tablets, so they've been bought up cheap by Chinese factories that hide behind various Aliexpress brands and put to use in mains only devices like this and mini PCs?
A few years ago no one would be too worried about idle power consumption, although perhaps they were indirectly by trying to manage CPU temperatures, which is directly affected by C-States and Package C-States as if they aren't working or not working optimally, more power is used and more heat is generated. Now given the costs some of us pay for electricity, we are taking an interest in idle power consumption.
The other issue with running these chips with C-States disabled is Intel do not guarantee their CPUs for longevity, they are designed to have C-States being entered, so we are potentially running these chips 24/7 with no C-States being entered just to have them fail early, but then that's built in obsolescence and no one seems to expect these cheap devices to last more than a couple of years anyway.
If any representative from these Chinese factories are reading this, now is your chance to set the record straight and explain what is going on.