Looking at the camera list and the fact it doesn't need new firmware, they're probably just using the existing tethering preview functionality.

The same can be achieved with gphoto2 piped to v4l2loopback (using ffmpeg to transcode). Something like:

    $ sudo modprobe v4l2loopback exclusive_caps=1 
    
    $ gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0

I think this is essentially the same thing Nikon is doing as well with the beta webcam utility.

Yeah, no. I don't think I've ever seen any kind of support for Linux from Sony. I have to dust off my ancient windows laptop whenever I want to upgrade the firmware on my cameras.