I suggest looking, maybe, at ALAC as well, even though it is generally slept on.
It is open source now just like FLAC, and actually has built-in support in Windows and many Linux music players despite being an Apple format, making it somewhat more universally compatible than FLAC (which isn’t supported in iOS or macOS).
In my school days I was able to add FLAC support to an iPod Touch 4th gen with a quick Cydia module(?) download. I'm skeptical of your claim that macOS doesn't support FLAC. I'm sure mpv and other programs can play it fine. Do you just mean support in the default-installed macOS software? That seems like pretty limiting criteria. I wouldn't expect something like Windows Media Player to cover all that much either.
It is open source now just like FLAC, and actually has built-in support in Windows and many Linux music players despite being an Apple format, making it somewhat more universally compatible than FLAC (which isn’t supported in iOS or macOS).