I think this issue is how ropieee is reporting the dac capability or are you also having this issue on ROCK? Not all builds of Linux fully support all DSD formats and rates, and might only be recognized as DoP capable at one rate lower than you might hope. If harry can get your feedback this might be the best option as Roon rock OS updates are not so often.
You might also reach out to the seller or manufacturer to ask them about their Linux support for DDD
It has to be a version of Linux that has been patched to see the Korg as a DSD native device or be sufficiently old and stable to be included in LTS versions. ROCK and Ropieee are ahead of the curve here being purpose designed for USB connection for music reproduction. What is interesting is that the screen shot shows the Korg as an unidentified device. That most certainly should not be the case. You should see a 10R shaped icon.
I noticed in this screenshot your device is not identified, can you try clicking on “Identify this device” and then selecting the Korg DS-DAC-10R from the menu?
This means that it would work with Mac and Linux in general, not that this device has Native DSD support for Mac/Linux. For Native DSD to work, it has to be patched into the ROCK Kernel.
I would try DoP output as @wklie suggests and confirm that works as expected first.
It still doesn’t address the issue of the fact the Korg is being marketed as Roon Ready but doesn’t appear to be. Has there been an issue with its certification?