default or selected kernelversion does not have config value CONFIG_IIO_ST_HWMON.
Result is shown for kernelversion 5.4.159

Hwmon driver that uses channels specified via iio maps

modulename: iio_hwmon.ko

configname: CONFIG_IIO_ST_HWMON

Linux Kernel Configuration
└─>Device Drivers
└─>Staging drivers
└─>IIO staging drivers
└─>Hardware Monitoring support
└─>Hwmon driver that uses channels specified via iio maps
In linux kernel since version 3.4 (release Date: 2012-05-20)  
This is a platform driver that in combination with a suitable
map allows IIO devices to provide basic hwmon functionality
for those channels specified in the map.

source code: