Nobody has replied in at least an hour so I think it's about time I clarify why this question was asked.
Most people have been leaning towards the distinction between low and high fantasy being akin to hard and soft sci-fi, respectively. Low fantasy is grounded, often a little gritty, closer to earth. High fantasy is set in highly magical worlds where the impossible is more common than you'd think and everything is at least a little larger than life.
The truth of the matter is, however, that low and high fantasy include stories on both ends of that scale of overall magic level and tone.
According to the 20th-century literary analysts who defined the term, the difference between low and high fantasy is that low fantasy is set in the "primary" world, a world that appears to be ours on the surface but where the supernatural is lurking around the corner, while high fantasy is set in another "secondary" world where the supernatural is part of life.
Tone does NOT play into this. Joss Whedon and writers influenced by him are well known for their urban fantasy with a very particular brand of humor and off the wall action, and their work (barring the MCU) is low fantasy because it assumes a world that appears to resemble ours on the surface, with the off the wall stuff all being hidden. Buffy the Vampire Slayer and the Dresden Files are both low fantasy. Meanwhile, gritty, sword and sorcery-influenced fantasy works where magic exists but is terrifying and obscure like Conan the Barbarian and Game of Thrones are high fantasy.
The definition of low and high fantasy you're familiar with, where low fantasy is low magic and low on steroids while high fantasy is the opposite, was invented by RPG designers who were looking for a useful way to categorize campaign styles. That older, literary definition has mostly fallen into obscurity, apparently because it's more useful when categorizing books.
Except, speaking personally, as a writer, I don't even really agree with that. J.R.R. Tolkien was in the business of writing fantasy stories before there was even a word for them (in addition to being a linguist of course), and he vehemently disagreed that Lord of the Rings was high fantasy. Yet to these literary analysts, Middle-Earth was typal high fantasy. To J.R.R. Tolkien, he was writing realistic fiction that just so happened to have magic in it, and a lot of modern literary analysts agree with him and discuss how his work would be more accurately classified as low fantasy, albeit under this more modern definition that more accurately accounts for things like "tone" and "style" that both authors and readers tend to care more about when it comes to genre fiction.
None of you have landed on "low fantasy" being "intrusion fantasy", and yet I have gotten into long arguments about if Game of Thrones is high fantasy or not. Maybe it's just because this newer definition has supplanted the old one in terms of how well-known it's become, but we really ought to put the older one to rest.