Were the 2021 Samsungs the ones that have a bug with videos and multiple audio streams where the audio track selection API provided by Samsung doesn’t work on that hardware forcing Plex to transcode those audio formats to AAC? Some combination of those search terms should find an answer in these forums. In either case sorry to hear your nice TV isn’t playing well with Plex.
Your other questions about PCM and AAC specifics would be a guess. So I’ll defer.
