There are some subtitled interviews with Kajiura Yuki about her process. Some of the key takeaway is that she writes about 10 times as many compositions as the number of songs she's published, she listens to a ton of music herself from a lot of highly varied sources, and she starts with the images/film cuts she's given and comes up with something that "fits."

Kanno Youko subbed interviews are much harder to find, at least back then for Cowboy Bebop, she just wtote an insane amount of songs, and then the sound direction and director used what they think fits, and while she din't always agree with their choices for particular scenes, she wasn't particularly upset either.

Edgerunners...it is less clear on. Akira Yamaoka is credited for the music, but a lot of it is lifted right from the game which is credited largely to Marcin Przybyłowicz, P.T. Adamczyk, and Paul Leonard-Morgan. They're cited in some game interviews about the music as just listening to a ton of it again.

So...loads and loads of research.