I want Plex to stream my FLAC music without losing quality but there doesn’t seem to be any setting for this in the iOS app or in the web interface - the advice I found in this article on optimising audio also seems out of date - the settings/audio section does not exist
This article applies to the Plex Media Player. Which doesn’t run on iOS nor in a web browser.
If you are in the same local network like your server, FLAC will play directly both in the web app and on iOS (AFAIK, I don’t have an iDevice to verify but I think it does. The iOS app got support to directly play FLACs some months ago).
If you are however in a remote network, the music will get transcoded in the iOS app.
The web app will continue to play the flacs directly - at least when using a desktop web browser.