default or selected kernelversion does not have config value CONFIG_NET_QOS.
Result is shown for kernelversion 5.4.123

QoS support

configname: CONFIG_NET_QOS

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>QoS and/or fair queueing
└─>QoS support
In linux kernel since version 2.6.12  
Say Y here if you want to include Quality Of Service scheduling
features, which means that you will be able to request certain
rate-of-flow limits for your network devices.

This Quality of Service (QoS) support will enable you to use
Differentiated Services (diffserv) and Resource Reservation Protocol
(RSVP) on your Linux router if you also say Y to "Packet classifier
API" and to some classifiers below. Documentation and software is at

Note that the answer to this question won't directly affect the
kernel: saying N will just cause the configurator to skip all
the questions about QoS support.