FLAC is FLAC is FLAC, its normally compressed in storage (various levels & default is 5) but it makes no difference as it’s unpacked & is full quality lossless when sent to the streamer.
Question - why use Plex, its a big program (uses a lot of resources) & is designed for video. Personally I did not like it & found Minim, & now Asset, easier in all aspects
Nice question Mike … it’s the first media server I found and initially wanted to stream video on the smartphones of my kids and on my smart TV. I then realized it could also stream FLAC files…