Where does the computer branding in KDE settings come from?
The settings on KDE show this info about my computer after buying a used motherboard. Apparently it came from a prebuilt, though it is a standard ASUS board. Where does this branding come from and is it possible to remove it?
This is part of the motherboard and can only be changed with specific tools from the manufacturer. Back in the days there was AMIDEDOS as a dos tool to change it in AMI Bios. You would need to find out, what tool can be used to change it in your UEFI. However, it's possible that those tools are not available to the public.
From the system's DMI. You can check it yourself with dmidecode. Those values are largely unchangeable, and those that are, will probably require a tool from the vendor to change, which are usually for internal use only within their company.
kinfocenter is an application in Plasma where you can see all kinds of information about your system. So no, they are not just adding k to random words like quantum in Ant-man. :)
You might be able to flash the retail BIOS to remove the OEM stuff, but often if it's running a specific OEM BIOS it'll block you from flashing a retail version.