Plex does automatic mixdown to stereo, if the player device knows that it only has 2 speakers.
It is also quite dependent on the type of Plex client, so please state what you are using on which hardware.
Mixdown to stereo doesn’t mean that it’s also reducing the dynamic range (the original dynamic range on DVD and Bluray can be quite high, which is what you are probably describing as “nolany”).
There is one type of Plex client which can perform dynamic range comprression on the fly An on-demand audio dynamics compressor for PMP and Plex HTPC
All other clients will not change the dynamic range. You will have to create an additional stereo audio track yourself and apply dynamic range compression: [How To] Downmix Surround Sound To AAC Stereo Properly (using FFmpeg Batch Converter)
