I think the "Filogic 820" branding may actually apply to the combination of the MT7981B SoC and the MT7976C NIC. https://wikidevi.wi-cat.ru/MediaTek seems to have actual detailed specs for these chips. It looks like the MT7981B is what has the ARM Cortex-A53 cores to run Linux, Ethernet, PCIe, and a 2x3:2 radio. The MT7976C is just a NIC with no application processor cores, but it has both a 2.4GHz and 5/6GHz radio. A NIC with two separate radios seems to be a relatively recent development, probably spurred by increased demand for tri-band routers after the opening of the 6GHz band.