Netgear R7800 MU-MIMO

Hi everybody,

I installed OpenWRT on a Netgear R7800.
When setting the router as an access point, it seems that it does not use MU-MIMO, even if I enable it through the hostapd configuration file and I also see it enabled checking the configurations.
The router sends to the clients NDP packets with "Feedback Type: SU feedback requested" while I expect MU feedback to be asked for.
Does anyone know the reason for that behavior?

Thank you in advance.