I used to be interested in fashion partially from some consumer discretionary / luxury sector vampire sorcery investment analysis stuff but also from sponsoring art and literary journals and attending some fashion exhibitions (tragic romance suppressed tearful sob
>>5417160 ).
Another cool source of inspiration is the lookbooks of various collections. You can just start by usual search etc if you do not know any already, some of these designers have completely insane avant garde visual ideas that will make you unlearn how to perceive shapes, colours and outlines in the world.
I guess this is why I really like Zak Smith artpunk rpgs, you can see from the way he draws his art in his ttrpg books he has thought about design and aesthetics a lot. With my weird setting in the Lightning Sea and the Highborn fashion I am thinking of the dark Gareth Pugh look, maybe early Alexander Mcqueen when he was still alive with Isabella Blow still alive, Iris van Herpen cathedral 3d printed wooden dress I mentioned on the other qtg and maybe a bit of Issey Miyake geometrical construction. Fashion is basically another language, you do not have to wear it to understand it. I was also told by various ateliers condescendingly that good fashion is architectural; fashion is NOT COSTUME. But these days we have cosplay hee hee (look, how many shares can you get out of tightly laced corsets and bosom) and some designers are indeed influenced by that.
So basically you can do some image searches of fashion lookbook collections, and use those shapes to inspire some NPCs / various social strata etc, or just guide the look of your world.
Here is some Gareth Pugh (annoying slideshow)
https://www.anothermag.com/fashion-beauty/12811/gareth-pugh-interview-lfw-ss-21-the-reconstruction-nick-knight-jon-emmony>tldr; fashion urgh so gay>watch Zoolander>just play the Paris level in HITMAN where you can assassinate that fashion designer guy using the light rig on the catwalk runway 