Because it’s lossy, period. You may not notice it if you’re not looking hard enough; but you wouldn’t accept a .zip file of a word doc that was missing letters or words in the document. You’d use lossless compression.
I’m not saying there’s no use for opus- just that if your goal is a high quality listening experience, that ain’t it.
That's like saying cars are crap because it's not as powerful as a truck. Both are completely different classes of vehicles optimizing for different use cases. So are lossy vs lossless codecs, you can't just say one is superior to the other without specifying the use case.
For instance, I've got a navidrome instance with all my music library accessible from anywhere in the world trough my phone. However there are situations where I may not have internet any connection, so I use the app on the phone (Tempo) to mark the songs I want to be downloaded and available even when offline, but my phone storage wouldn't hold even a quarter of my playlists if I went with the original encode of the songs (mostly lossless flacs), so I instead set it to download a transcoded Opus 128kbps version of it all and it fits on my phone with room to spare. It sound pretty damn good trough my admittedly average IEMs and I get the benefit of offline playback. Even if you somehow had the absolute best playback system connected to my phone you might be able to tell the difference, but it beats not having to rely on internet connectivity.
That's a bad illustration. The letters are there.. they're just slightly lower rez. Like going from a 256x256 space per letter to 128x128. Is there a difference? sure. Can you read it perfectly fine.. of course.
You could probably argue that these are handwritten letters but the argument still stands.
If you decide to stream with a lower bitrate in Plexamp, it transcodes to Opus.
You should not encode the files, just use Plex or Jellyfin and choose a lower bitrate when playing with your phone. Jellyfin uses AAC and Plexamp uses Opus.