Don't.
Academia is, in general, conservative with respect to ideas. Whole brain emulation is viewed by many as weird, speculative, and maybe crank pseudoscience.
The exception is if you apply to a school where there are professors explicitly pursuing research with the goal of achieving whole brain emulation. Then mention it as it will help you stand out and get in with them.
Otherwise, keep it to yourself at least until you're already working on your dissertation.
As for other problems you mention, I get the sense that AI risk is becoming mainstream. Certain kinds of anti-aging research are already mainstream, but the most radical kind isn't. Genetic modification is mainstream in some ways, not in others. Cryonics is definitely still not mainstream (there's active effort to keep cryobiology separate from it). Really just depends on the specific topic and how the majority of the field views it.
I am applying to grad school for neuroscience or adjacent fields and I want to do work on connectomics, single cell computation, or c elegans uploading specifically in service of wbe in general. Some labs, like this one at leeds, are in favor of it at least in the case of c elegans, but even there I'm not sure how they feel about it for humans. Others are just places developing imaging techniques or doing electrophysiology experiments that will be useful to wbe but it isn't their mission statement. I feel weird and disingenuous leaving it out as so many applications as for you motivation, your long term goals, or what got you interested in applying but at the same time it still feels a little taboo. If anyone has advice that's great. Even a sweeping binary of saying not to mention it at all would be useful. If you have experience applying yourself or are involved in this in some other way I would appreciate knowing that. If this is too specific, I am curious to hear about general thoughts on mentioning big but kind of out there problems in academia (AI risk obviously, anti-aging research, genetic modification of humans, cryonics, etc.)