Open HandBrake
Click Open Source and select your video file
Choose an output destination and file name
Set the output format to MP4 or MKV
Go to the Audio tab
Remove any unwanted audio tracks
Keep the audio track you want to extract
Set the audio codec if needed
Adjust bitrate, mixdown, and sample rate if needed
Start the encode
Find the extracted audio in the output file
If you need audio only, use a compatible container and keep only the audio track