default or selected kernelversion does not have config value CONFIG_CLONE_BACKWARDS3.
Result is shown for kernelversion 6.9.9

CONFIG_CLONE_BACKWARDS3 (not configurable)

configname: CONFIG_CLONE_BACKWARDS3

Linux Kernel Configuration
└─>General architecture-dependent options
└─>CLONE_BACKWARDS3
In linux kernel since version 3.10.2 (release Date: 2013-07-21)  
Architecture has tls passed as the 3rd argument of clone(2),
not the 5th one.