Hi - I responded to your PM, but sharing the info here as well as it may be helpful to others:
The OKX encoder is a custom module built into the ORC service, which can be played back in ORBX Media apps and players (including Samsung Internet on Gear VR), The encoding takes many minutes per frame, and can be longer than render times (in some scenes), so we use the CPU do the OKX encode on a finished frame while the GPU renders the next one to make it appear 'free' on ORC (we may take the same approach with AI denoising as optional output in 3.09 for max efficiency on ORC).
We've not yet directly exposed OKX file format export beyond ORC for support reasons (and also because it's device/GPU specific), but we are working with FB, Unity. KHR/glTF group, MPEG and others to help make the technique (using GL/GPU shaders as codec) part of a proper standard.
That being said, you should see OKX output options on ORC along with EXR/PNG. Let me discuss this with ORC team and get this sorted out ASAP. Thank you for bringing this to our attention.