Man pages matching name mlx5dv_devx_umem_dereg in section 3:

mlx5dv_devx_umem_dereg.3.en	debian 10 / libibverbs-dev
mlx5dv_devx_umem_dereg.3.en	debian 11 / libibverbs-dev
mlx5dv_devx_umem_dereg.3.en	debian 12 / libibverbs-dev