An odd pair of chromosomes makes it harder than being off by a pair. Mules are unbreedable due to their odd number of chromosomes.

We have successfully bred with species further apart, including an alpaca and a llama.

So yes all the science points to it being possible with humans, but ethically we can’t possibly do that.

And it is not one more mutation to add an extra chromosome. It’s a loooot more.

It may be just the selection of the current drive you’re in? Does it show an x on another drive when you select it?