Plex unable to transcode Opus audio

I have a file encoded with Opus. On paper, Plex should transcode it to something else when playing on an unsupported client, like my 2019 Samsung TV. However I simply get an “unknown playback error” whenever I try to play it. Transcoding other formats works fine. And playing the file on a device that supports Opus audio is also fine.

I tried going to Plex forums for this with logs and got no response. Does anyone have an idea of why this wound occur? PMS is on Ubuntu.