CSD97394Q4M: What ist the value of the sink current? I mean the continuous current from the bottom MOSFET.

Are you talking about the Low-Side FET? When PWM is low, Low-Side FET will be turned on and flow the load current; while if Low-Side FET is off, no current will flow through LS FET.

Thanks!

Yes, the LS FET. I want to know the permissible highest current at the low-side FET. For example, in datasheet from TPS54821 you can find Low-side switch sinking current limit,  that is the question.