FLAC like other lossless formats has its export bit depth set by the export choice. The Default Sample Format in Quality Preferences plays no part .
Import of FLAC (using libflac) could be considered more “logical” than WAV in that you don’t import at a higher bit depth than the Preference bit depth or the file bit depth:
Default
Sample Format File bit depth Imports as
16 16 16
16 24 24
24 16 24
24 24 24
32 16 32
32 24 32
On Linux, FLAC is imported by the WAV importer (libsndfile) by default so I assume but I have not tested that the behaviour will be as for WAV.
Gale