public RayTracingAccelerationStructureBuildFlags buildFlags { readonly get; set; }

For acceleration structure implementations that use a two-level hierarchy, for example DirectX Raytracing (DXR), Unity uses these flags to build the top-level acceleration structure (TLAS).

To customize the flags Unity uses to build the bottom-level acceleration structures (BLAS), use Renderer settings or the parameters in the RayTracingAccelerationStructure.AddInstance method.