default or selected kernelversion does not have config value CONFIG_ISDN_HDLC.
Result is shown for kernelversion 6.8.2
CONFIG_ISDN_HDLC (not configurable)
modulename: isdnhdlc.ko
configname: CONFIG_ISDN_HDLC
Linux Kernel Configuration
└─>Device Drivers
└─>ISDN support
└─>ISDN_HDLC