Betaflight and Cleanflight have a "uptilt compensation" feature that automatically adjusts the yaw axis to make your quadcopter handle as if it didn't have any FPV camera uptilt. But you can learn to do this manually, and get better results. I'll show you how!
* Betaflight uptilt compensation: https://www.youtube.com/watch?v=gEcWxHIH378 (Note: this feature is now in the GUI, in the configuration tab. The CLI option referenced in the video doesn't exist any more.)