This short video will show you how to use OBS Studio (Open Broadcaster Software Studio) to create .mp4 files which have multiple discrete (separated) audio tracks.
This allows you to import the .mp4 into your video editing software and deal with both audio channel separately. You can apply gain or effects independently, and split/cut out parts of either the game audio or microphone audio sources without affecting the other sources.
Let me know if you have any questions, please like and subscribe if it helped you!