default or selected kernelversion does not have config value CONFIG_NTSC_640x480.
Result is shown for kernelversion 6.7-rc3

NTSC 640x480 (Experimental)

configname: CONFIG_NTSC_640x480

Video mode support
└─>NTSC 640x480 (Experimental)
In linux kernel since version 2.6.38 (release Date: 2011-03-14)