Qos Upstream and Downstream greyed out?

Think of QoS as a cop controlling traffic on the main road into and out of town.  The cop wouldn't be very effective controlling only a subset of all traffic.  An Access Point (AP) is typically not in a position to handle all Internet traffic arriving or leaving your house.  Because of this, QoS is usually not available as an option.

In a home network, it makes the most sense to apply QoS at the router which handles all Internet traffic as it arrives or leaves your house.  Your modem may have a router built into it, in which case, QoS should be enabled there.  If your modem doesn't have a router but you, instead, have a separate router connected directly to the modem, then QoS should be enabled there.

While the R7800 is a router, putting it into AP mode disables many functions, including the firewall, NAT and, of course, QoS.  If you want to use QoS on the R7800, then disable AP mode, but you should connect all devices through it and you should disable all routing functions in all other devices.  Having a single device functioning as a router is recommended for the vast majority of home networks.