I have done it.
First did you go to the IO set up and under the USB tab select L & R on tracks 1 & 2?
Have you confirmed that your software is picking off tracks/channels 1 & 2 from the
USB B multitrack out?
I my case a couple times I was connected to a computer that was running OBS and OBS was seeing tracks/channels 1 & 2 and I set them to the L R main mix.
Those were a live stream only event, no house PA to speak of.
Another time I was setting up a system and in that case I set up a separate mix to feed their live stream so some mix balance adjustments could be made.
I that case I’m not sure of the software they running but it also picked off tracks 1 & 2 and worked fine.
Are you also mixing for a live PA or is this for a ZOOM event only?
For testing use the mixers tone generator, if a live PA is involved you may want to turn off the system when testing or set up a separate mix.