Your premise of "tablets are on topic" is flawed. The top voted answer states that we should allow tablet questions where those tablets run a "real" generic operating system. iOS and Android devices are off topic by the criteria established there, as would be their hardware. Windows on Arm is allowed because the OS shares a lot of functionality with the "full" version of Windows and require the same solutions.
We also allow Raspberry Pi questions where the problems are about using Linux on it. It is essentially an Arm Linux computer and as such the OS is on topic, but none of the hardware is replaceable or generic. There is nothing "field servicable" about the hardware and any relevant information on it is available on the product website.
Continuing in that vein... If your questions for the C64Mini were about using it as a Linux computer then fine, generic Linux questions are on topic here. But asking how to hack a PCIe 4G cellular or WiFi module into the physical hardware would be off topic.
Questions about pre-release hardware that might change at any time before final release can make for a fun game of catch the rabbit, but can lead to a rather unhelpful discussion answer saying "well they changed this at the 11th hour and so this is the real answer now but back in my day..."
You should preferably ask questions about problems you ate currently facing while using something in front of you.
We also don't really need a massive long series of questions cataloguing every tiny Arm/x84/MIPS device stating which particular processor they use. It shouldn't be relevant to using the device as a real computer.