Opus is better than aac, but above HD, only AAC is selected, so that audio and video can be selected separately.

After I tried your software,I use MiPony to download Opus, compared with AAC using 4kvideodownloader.
Opus is better than aac.
http://opus-codec.org/comparison/

Below I have left the youtube URL of the video to compare with bitrate:
youtube URL:
https://www.youtube.com/watch?v=cKF5Y1S7Ujs&list=PLwtGjY1jrSDccJuPIqVHoXPHovd1RBJQ5&index=1

Audio comparison chart:
https://imgur.com/oxwGP70