CONFIG_BINFMT_AOUT32 is not available for thedefaultarchitecture x86.
Result is shown for architecture sparc64
default or selected kernelversion does not have config value CONFIG_BINFMT_AOUT32.
Result is shown for kernelversion 5.4.123

Kernel support for 32-bit (ie. SunOS) a.out binaries

modulename: binfmt_aout32.ko

configname: CONFIG_BINFMT_AOUT32

Linux/UltraSPARC Kernel Configuration
└─>General machine setup
└─>Kernel support for 32-bit (ie. SunOS) a.out binaries
In linux kernel since version 2.6.12  
This allows you to run 32-bit a.out format binaries on your Ultra.
If you want to run SunOS binaries (see SunOS binary emulation below)
or other a.out binaries, say Y. If unsure, say N.

source code: