default or selected kernelversion does not have config value CONFIG_AD9850.
Result is shown for kernelversion 5.9.9

Analog Devices ad9850/1 driver

modulename: ad9850.ko
configname: CONFIG_AD9850

Linux Kernel Configuration
└─> Device Drivers
└─> Staging drivers
└─> IIO staging drivers
└─> Direct Digital Synthesis
└─> SPI support
└─> Analog Devices ad9850/1 driver

Say yes here to build support for Analog Devices DDS chip
ad9850/1, provides direct access via sysfs.

source code: