Hi, I just wonder maybe there is unpopulated space on PCB for second (possibly larger, NAND) SPI flash?
https://fccid.io/2APRGRT02/Internal-Photos/Internal-photos-6580724.pdf#page=3
even the DTS file has something disabled here https://github.com/openwrt/openwrt/blob/main/target/linux/mediatek/dts/mt7981b-cudy-wr3000-v1.dts#L127
The 16MB NOR spi is quite small so maybe they planned this to grow and have NOR+NAND setup?