"Dark academia" is meaningless as an aesthetic term.
As a fiction genre, it makes sense. What's the tone? Dark. Where is this taking place? Academia (a university, museum, archive, high school, or other Place of More-Or-Less Public StudyTM). Information is conveyed and it has a clear meaning. Easy to understand.
As an aesthetic descriptor, it falls apart. Most people use it to connote an aesthetic centered somewhere between the late 19th century and the 1960s- but only with buildings that are 1920s or older -and heavily leaning on mid-20th-century vintage fashion inspiration, old-fashioned note-taking and study tools, particularly vintage-looking cafes and bakeries, etc. The problem is, none of that is related to academia by nature. Academia doesn't have an aesthetic; institutions of higher learning generally follow the architecture that was popular in a given time period, and are full of people dressing normally for their present day.
Usually what they mean is "dark \[insert vintage period here\]," but because they saw those items first in the context of dark academia fiction, they tend to carry the term outside the realm of describing a story.
This leads to absolutely insane things being labeled as "dark academia": moodily-lit photos of baked goods, any marble statuary regardless of context, any old buildings in the vague time period adherents of this style tend to focus on, etc. I've seen the term applied to an Art Deco theatre lobby. Was it a university theatre? Nope. Was it a theatre reconstructed in a museum? Not at all. It was a random professional theatre that operated 100% independently. "Dark Academia." Somehow.
This is a molehill I will defend to the death. #conversation