What Low Fantasy actually originally meant in like the 1920s when the terms came about, in contrast with High Fantasy was that Low Fantasy took place "here" on our Earth, but with Fantastical Elements, while High Fantasy took place in constructed worlds. OVertime this distinction became less important or diagnostic of the stories the supposedly different subgenres told, so it was dropped, and High Fantasy became anything where there was a lot of magic and a general Noblebright tone, while Low Fantasy became mostly synonymous with a gritty tone.
TL;DR, originally it was
Low Fantasy: Harry Potter
High Fantasy: Lord of the Rings
Low Fantasy: Song of Ice and Fire
High Fantasy: Lord of the Rings.