CONFIG_ARM_THUMB is not available for the default architecture x86.
Result is shown for architecture arm

Support Thumb user binaries

configname: CONFIG_ARM_THUMB

Linux Kernel Configuration
└─> Support Thumb user binaries

Say Y if you want to include kernel support for running user space
Thumb binaries.

The Thumb instruction set is a compressed form of the standard ARM
instruction set resulting in smaller binaries at the expense of
slightly less efficient code.

If this option is disabled, and you run userspace that switches to
Thumb mode, signal handling will not work correctly, resulting in
segmentation faults or illegal instruction aborts.

If you don't know what this all is, saying Y is a safe choice.