I wanted to use the soundtrack from a AAA game but I’m worried about copyright. Is there a fair use or is there a way to contact the composers or developers to let me use their music?
It’s possible, that posting on the AAA studios forum (hopefully they have one)
about wanting to use, a certain game ost from their game, in your game, might
be a better option. There’s a chance the devs or even better, the composer
might reply to you. Or they might link you to the composers website.
But hope for the best of luck. 
Because in most cases, most AAA game dev studios and their music composers
don’t always allow their game music, to be featured in other games.
Especially, if it’s their rivals games.
Okay. I’m curious, what soundtrack did you want to use?
I’ve wanted to use the music from Deus Ex Mankind Divided : Breach. The game flopped hard and it has good music, I guessed they wouldn’t give a shit since its all but wasted resources.
They would. Whether or not the game did well on sales is not relevant to whether or not you can use content from it.
They still own the rights to it and will sue you if they find out you’re using it.
As a general rule of thumb when creating anything (software, videos, documents, websites, etc.) you should never include content unless:
- You made it yourself.
- You paid for it / paid someone to make it for you.
- You were given permission specifically by the developer/publisher or whoever owns the license to use it for free.
- It is explicitly stated that the content is royalty free.
It’s better to settle for less than to have a massive company come at you with a cease & desist.