default or selected kernelversion does not have config value CONFIG_ATMEL_TCB_CLKSRC_BLOCK.
Result is shown for kernelversion 5.9.8

TC Block


Linux Kernel Configuration
└─> Device Drivers
└─> Misc devices
└─> TC Block

Some chips provide more than one TC block, so you have the
choice of which one to use for the clock framework. The other
TC can be used for other purposes, such as PWM generation and
interval timing.