I'm using a Samsung Galaxy S10 (US version with SD855 chipset), and when playing back Hi-Res FLAC I can change the sample rate (ie 96khz) but not the sample format, it's stuck at 16-bit. I'm pretty sure the S10 supports at least 96khz/24-bit.
Also, perhaps more of a feature request, is there a way to just always use the sample rate of the source file? Now whenever a sample rate is picked every file plays at that rate, which often means that a 44.1khz file is upsampled, requiring more processing power and draining the battery more quickly. It's my understanding that this is deliberate on your part as it can cause issues with gapless playback and buffering when switching between two files with different sample rates. I'd however ask you to reconsider and at least provide it as an option while warning users of some of the downsides (gapless playback typically only matters between files on the same album and those will usually have the same sample and bit rate anyway).
The build I'm using is 823-play (full version).