See a similar thread from May 2019:
No HLS support has been added since although I suspect that it would only happen when the next Mosaic version is released (if then as I am presuming it may require licensing from Apple).
As for FLAC Mosaic only lists AAC 320K feeds for the various versions of Radio Paradise. Carrying out a dipstick test of the stations offered as “High Quality” these all appear to be stations using higher rate lossy codecs.
As Andrew has already stated that FLAC is technically supported by Mosaic then this points to the radio aggregator (airable) not having FLAC links in their catalogue. If that is so there isn’t anything that dCS can do about it beyond asking.
As this topic has been going on for well over a year now I wonder if dCS would kindly give an update on the situation?