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

HCI UART (PC Card) device driver

modulename: btuart_cs.ko

configname: CONFIG_BT_HCIBTUART

Linux Kernel Configuration
└─>Networking support
└─>Bluetooth subsystem support
└─>Bluetooth device drivers
└─>HCI UART (PC Card) device driver
In linux kernel since version 2.6.12  
Bluetooth HCI UART (PC Card) driver.
This driver provides support for Bluetooth PCMCIA devices with
an UART interface:
Xircom CreditCard Bluetooth Adapter
Xircom RealPort2 Bluetooth Adapter
Sphinx PICO Card
H-Soft blue+Card
Cyber-blue Compact Flash Card

Say Y here to compile support for HCI UART devices into the
kernel or say M to compile it as module (btuart_cs).

source code: