default or selected kernelversion does not have config value CONFIG_MLX5_ACCEL.
Result is shown for kernelversion 6.9.9

CONFIG_MLX5_ACCEL (not configurable)

configname: CONFIG_MLX5_ACCEL

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Ethernet driver support
└─>MLX5_ACCEL
In linux kernel since version 3.10 (release Date: 2013-06-30)