RAX120 Guest network client isolation

Recently bought a RAX120, using it in AP mode with firmware V1.0.1.122

I can't understand why there is no way to enable wireless client isolation in the Guest network when in AP mode. The old WNDR4500 I just replaced had that option and it was released in 2011. My D6200 has that option and it's also a few years old.

There's a ton of new capabilities in the RAX120, but I would think network security options would be stronger now, not greyed out. If it's just a firmware issue, just enable it back.