connecting a UART console it shows (output depending on the hardware installed)
Detected Device ID 6820
board SerDes lanes topology details:
If that is any indication to go by it would seem to be single lane (x1) for each PCIe slot.
If it is indeed PCIe3 x1 for the slot with the Wlan card it would mean max. 0.9846 Gbyte/s (less protocol overhead) and thus render 5GHz ax superfluous in terms of expanding bandwidth on that spectrum.
ahci-mvebu f10a8000.sata: AHCI 0001.0000 32 slots 2 ports 6 Gbps
it would seem that the speed tags listed in the above topology table are indicative of the PCIe link’s bandwidth in Gbps.
SGMII2 = Serial Gigabit MediaI Independent Interface and 2 likely indicating 2.5GBASE-T (over legacy Cat5e/6 cabling) according to IEEE 802.3bz
Thus the speed tag 0.
Further reading on IEEE 802.3bz for the interested