default or selected kernelversion does not have config value CONFIG_MLXREG_DPU.
Result is shown for kernelversion 6.16-rc7

Nvidia Data Processor Unit platform driver support

modulename: mlxreg-dpu.ko

configname: CONFIG_MLXREG_DPU

Linux Kernel Configuration
└─>Device Drivers
└─>Platform support for Mellanox hardware
└─>Nvidia Data Processor Unit platform driver support
In linux kernel since version 6.1.145 (release Date: 2025-07-14)  
This driver provides support for the Nvidia BF3 Data Processor Units,
which are the part of SN4280 Ethernet smart switch systems
providing a high performance switching solution for Enterprise Data
Centers (EDC) for building Ethernet based clusters, High-Performance
Computing (HPC) and embedded environments.

If you have a Nvidia smart switch system, say Y or M here.

source code: