DaVinci doesn’t support AAC audio, it’s easiest to re-encode it using FFmpeg to use PCM. Here’s an example on Linux:
ffmpeg -i input.mp4 -c:v copy -c:a pcm_s16le fixed_output.mkv
The output will have audio when imported into DaVinci Resolve.
Alternatively, Shutter Encoder has been recommended a few times in the DaVinci forums.