default or selected kernelversion does not have config value CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT.
Result is shown for kernelversion 6.7-rc3

Hotplugged memory limit (in GiB) for a PV guest

configname: CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT

Linux Kernel Configuration
└─>Device Drivers
└─>Xen driver support
└─>Hotplugged memory limit (in GiB) for a PV guest
In linux kernel since version 3.19.5 (release Date: 2015-04-19)  
Maxmium amount of memory (in GiB) that a PV guest can be
expanded to when using memory hotplug.

A PV guest can have more memory than this limit if is
started with a larger maximum.

This value is used to allocate enough space in internal
tables needed for physical memory administration.