default or selected kernelversion does not have config value CONFIG_ATM_DUMMY.
Result is shown for kernelversion 6.0-rc7

Dummy ATM driver

modulename: adummy.ko
configname: CONFIG_ATM_DUMMY

Linux Kernel Configuration
└─> Device Drivers
└─> Network device support
└─> ATM drivers
└─> Dummy ATM driver

Dummy ATM driver. Useful for proxy signalling, testing,
and development. If unsure, say N.

source code: