If the board is already powered on, you can find the model by typing System Information
Then the package arrived.
Since this marking appears on several boards from the early-to-mid 2010s, "21 B6 E1 E2" is most commonly associated with or LGA 1150 socket motherboards supporting 2nd, 3rd, or 4th Generation Intel Core processors. intel desktop board 21 b6 e1 e2 specification
The D21-B6-E1-E2 offered a range of expansion slots, including one PCIe 3.0 x16 slot, one PCIe 3.0 x4 slot, and two PCIe 3.0 x1 slots. This allowed John to add a graphics card, sound card, or other peripherals to his system. For connectivity, the board featured a range of ports, including USB 3.2 Gen 1, USB 2.0, and Gigabit Ethernet. If the board is already powered on, you