Is there any species, other than humans, that is found all across the globe (i.e. geographically separated), and has not differentiated into subspecies? Wolves, elephants, tigers, bears, and foxes have all been categorized into multiple subspecies each, distinct but able to interbreed.

The definition of what constitutes a species is a human construct.

Two bird populations living in the same locale but divided by a mountain range therefore not naturally breeding with each other would classify as a different species, even if they could breed with each other.

So your question is hard to answer.

We dont categorize humans that way; not because humans are different but because of cultural norms.

The generous idea is that "subspecies" does not provide an anthropologist a useful lens to look at humanity, therefore we do not classify.

The alternative is that "subspecies" is too close to "race" for scientists, publishers, and funding bodies to touch, so its deliberately ignored.

How about Taraxacum officinale, the common dandelion?

It’s not quite all across the globe but pretty close, and is so adapted that it is not considered invasive any more in most places.

Do humans not fit the standards for being broken into multiple subspecies? I assumed that they would but "the science community" is too scared of the implications when idiots learn about it.

I look at a sumatran tiger and a Siberian tiger and I see a lot less variance than I see when I look at a pygmy, a Norwegian, an sentinel islander, and a han Chinese person

Not many. Part of why we are like this is extreme mobility. Even before modern times we were always good at getting around and seem to have a desire to roam. Or at least enough of us do to mix up those gene pools.

Dogs?

> ...distinct but able to interbreed

I mean people won't like the idea but that's not my point; what you describe variety in superficial traits while maintaining common traits

Applied to humans; skin color, eyes, dwarfism, hypertrichosis... can still interbreed

When it comes to categorization and taxonomy in leaky abstractions like languages the boundaries get a bit hand wavy and usually land on whatever fits the prevailing social desirability bias of the day

They have to be. The snail darter is genetically identical to another animal and is a separate species. Most likely different humans are as well.

Humans have, obviously. Just interbreeding with ancient species was enough to do it, even without separate evolution.