CONFIG_ETRAX_SERIAL is not available for thedefaultarchitecture x86.
Result is shown for architecture cris
default or selected kernelversion does not have config value CONFIG_ETRAX_SERIAL.
Result is shown for kernelversion 6.7-rc3

Serial-port support

modulename: crisv10.ko

configname: CONFIG_ETRAX_SERIAL

Linux Kernel Configuration
└─>Serial-port support
In linux kernel since version 2.6.12  
Enables the ETRAX 100 serial driver for ser0 (ttyS0)
You probably want this enabled.

source code: