default or selected kernelversion does not have config value CONFIG_FEC_8XX_LXT971_PHY.
Result is shown for kernelversion 5.19-rc1

Support LXT971/LXT972 PHY

configname: CONFIG_FEC_8XX_LXT971_PHY

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Ethernet (10 or 100Mbit)
└─>Support LXT971/LXT972 PHY
In linux kernel since version 2.6.20 (release Date: 2007-02-04)