For lowering the sample format, I believe that dithering is preferred to truncating. For example, PulseAudio does not seem to dither but PipeWire seems to dither.
PipeWire will replace PulseAudio and so the 16-bit FLAC files will be dithered if PipeWire outputs in 16 bits since VLC outputs them in 32 bits whether the sound is modified (for example equalized) or not.
For the 16-bit PCM files, VLC outputs them in 16 bits and so will not be dithered by PipeWire.