CONFIG_MODULES_SIZE is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

Size of modules/execmem area (In Mbytes)

configname: CONFIG_MODULES_SIZE

Linux Kernel Configuration
└─>Advanced setup
└─>Size of modules/execmem area (In Mbytes)
In linux kernel since version 6.1.112 (release Date: 2024-09-30)  
depends
CONFIG_PPC32