I have the same issue BTW.
It's not an issue. It's normal and expected.
The "BN" (board name) field of the "Board Info" dialog is filled when the Arduino board definition specifies a VID (vendor identifier) and PID (product identifier) for the board. For example, here is the VID/PID definition for the Arduino Nano:
The VID and PID are numbers provided by USB devices to identify the device. So if you plug a board into your computer that has any of the above VID/PID pairs, select the port of that board, and then check the "Board Info", it will say:
BN: Arduino Uno
The classic Nano uses a general purpose USB to TTL serial adapter chip (FTDI FT232). The Chinese Nano derivative boards use the WCH CH340. These chips have a VID/PID pair provided by the manufacture. So there is no way to know which Arduino board those chips are connected to, or even if it is an Arduino board (I have several consumer electronics devices that use FT232 connected to my computer). So it would be silly for the Nano board definition to specify the VID/PID of the FT232.
If you do want the ports created by general purpose USB to TTL serial chips to be identified by the Arduino IDE, you can install this 3rd party "zzInoVIDPID" boards platform:
The way the platform works is by defining a dummy board definition for each of the common general purpose USB to TTL serial chips, which are associated with their manufacturer provided VID/PID pairs. You don't actually use the boards (in fact they are hidden), they only provide convenient labeling in the Arduino IDE's Tools > Port menu for ports that are created by those chips:
Since I have so many serial ports on my computer, I find it extremely useful to have some identification of what they are in the Arduino IDE's Tools > Port menu, as provided by that boards platform.
Where can I learn more about "16u2
The official Uno and Mega boards use an ATmega16U2 microcontroller as a USB to TTL serial adapter. Since this is just a general purpose microcontroller, Arduino had to write a custom firmware for the ATmega16U2. That firmware defines a custom VID/PID pair that belongs to Arduino. They purchased that right from the USB Implementers Forum. Since Arduino can define custom, unique VID/PID pairs for each board, it makes sense to define the VID/PID pairs for those boards in the board definition. This is why, if you have a real Mega or a faithful clone, you will see a "BN" in the "Board Info" dialog when you have the port of your Mega selected from the Arduino IDE's Tools > Port menu.
or native USB"
Some microcontrollers have built in USB capabilities. The boards that use one of these microcontrollers don't need to use a separate USB to TTL serial adapter chip, The can just connect the USB socket on the board directly to the primary microcontroller.
The reason your Mega needs the ATmega16U2 (or CH340 on the Chinese derivatives) is because the primary ATmega2560 microcontroller doesn't have native USB capabilities. The ATmega16U2 does have native USB capabilities, so it can act as the USB adapter for the board.
The original native USB board was the Leonardo, which uses the ATmega32U4 microcontroller. The newer Arduino SAMD boards (e.g., MKR, Nano 33 IoT, Zero) use the ATSAMD21G18 microcontroller, which also have native USB capabilities. These boards are also able to do mouse and keyboard emulation. There are other microcontrollers used in Arduino compatible boards with native USB capability.
I think you now understand what the "VID" and "PID" fields of the Board Info dialog are. So that leaves "SN" (serial number). Some USB devices have a unique serial number that can be read by your computer. When available, that serial number is shown in this field.