default or selected kernelversion does not have config value CONFIG_DRM_CLIENT_SETUP.
Result is shown for kernelversion 6.6.75

CONFIG_DRM_CLIENT_SETUP (not configurable)

configname: CONFIG_DRM_CLIENT_SETUP

Linux Kernel Configuration
└─>Device Drivers
└─>Graphics support
└─>Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)
└─>DRM_CLIENT_SETUP
In linux kernel since version 5.4.290 (release Date: 2025-02-01)  
Enables the DRM client selection. DRM drivers that support the
default clients should select DRM_CLIENT_SELECTION instead.