default or selected kernelversion does not have config value CONFIG_VGACON_SOFT_SCROLLBACK_SIZE.
Result is shown for kernelversion 6.5.1

Scrollback Buffer Size (in KB)

configname: CONFIG_VGACON_SOFT_SCROLLBACK_SIZE

Linux Kernel Configuration
└─>Device Drivers
└─>Graphics support
└─>Console display driver support
└─>Scrollback Buffer Size (in KB)
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Enter the amount of System RAM to allocate for the scrollback
buffer. Each 64KB will give you approximately 16 80x25
screenfuls of scrollback buffer