default or selected kernelversion does not have config value CONFIG_MLX5_IPSEC.
Result is shown for kernelversion 6.9.9

Mellanox Technologies IPsec Connect-X support

configname: CONFIG_MLX5_IPSEC

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Ethernet driver support
└─>Mellanox Technologies IPsec Connect-X support
In linux kernel since version 5.1 (release Date: 2019-05-05)  
Build IPsec support for the Connect-X family of network cards by Mellanox
Technologies.
Note: If you select this option, the mlx5_core driver will include
IPsec support for the Connect-X family.