default or selected kernelversion does not have config value CONFIG_MEMTEST_BOOTPARAM.
Result is shown for kernelversion 5.19-rc1

Memtest boot parameter

configname: CONFIG_MEMTEST_BOOTPARAM

Linux Kernel Configuration for x86
└─>Processor type and features
└─>Memtest boot parameter
In linux kernel since version 2.6.26 (release Date: 2008-07-13)  
This option adds a kernel parameter 'memtest', which allows memtest
to be disabled at boot. If this option is selected, memtest
functionality can be disabled with memtest=0 on the kernel
command line. The purpose of this option is to allow a single
kernel image to be distributed with memtest built in, but not
necessarily enabled.

If you are unsure how to answer this question, answer Y.

depends
CONFIG_X86_64