default or selected kernelversion does not have config value CONFIG_LOOPBACK_TARGET_CDB_DEBUG.
Result is shown for kernelversion 5.6.18
TCM loopback fabric module CDB debug code
configname: CONFIG_LOOPBACK_TARGET_CDB_DEBUG
Linux Kernel Configuration
└─>Device Drivers
└─>Generic Target Core Mod (TCM) and ConfigFS Infrastructure
└─>TCM loopback fabric module CDB debug code
In linux kernel since version 2.6.39 (release Date: 2011-05-18)
Say Y here to enable the TCM loopback fabric module CDB debug code