Why doesn't an imported mp4 file with linked audio show the audio when dragged into the sequence

When an video with linked audio doesn’t show the audio in your sequence, it’s often because source patching for A1 isn’t enabled. Source Patching ensures that audio and video are placed on the correct tracks when added to the timeline.

For more details on track targeting and source patching, you can refer to Adobe’s official guide: Source Patching and Track Targeting.