It's in the changelog:
If your hardware has no L3HW Fasttrack support, then the parameter is no longer there. Here are the list of devices (highend CCR and CRS with Prestera 98DX8xxx / 98DX4xxx switch chips):
L3 Hardware Offloading | RouterOS Manual
If you have those devices, then if the setting is "on", you also won't see it in the export because the default value is now "on".