I think Itunes was the problem for FLAC. Other software will play FLAC files. Itunes will do it if you convert from FLAC to another file. I used AIFF (lossless file for my music file library). Apps for FLAC files? dBpoweramp (windows and mac), Golden Ear (ios), FLAC player (ios), Fluke (mac), Tonido (ios), TuneShell (ios), VOX. There are probably more. Also both IOS and Windows can be loaded on a MAC. Just partition the HD.
Do Macs Play FLAC?
My my understanding was always that they could not play FLAC encoded files. I just installed a Synology NAS. I have a Bluesound Vault 2 with about 300 CDs that were ripped in FLAC and was able to transfer the contents of the Vault 2 to the NAS. These show up as FLAC files in the NAS index. To my surprise, they play on my MAcAir, purchased in in 2013, via usb into a Bryston DAC3. I had assumed I would need a music playing program to make these files playable on the Mac. I have no FLAC converting software loaded onto the Mac