FLAC doesnt work in any apple devices

[apollolux]

I have just converted one flac file to ALAC(ext. m4a). The original FLAC audio file is 404.1 MB whereas apple lossless is 409.3 MB. Wondering why a little difference. Aren't they supposed to be same in size since they are lossless

They likely use slightly different algorithms for compression; think a replacement cipher, where one replaces the word "the" with the letter "a" while another replaces "the" with "a0" instead. FLAC offers more compression options and "features" than ALAC (which is likely why the FLAC is smaller), but usually compress audio to nearly the same size; for smaller files this difference is usually negligible (~20KB/minute or so), but since according to other posts around here BASE 2.1 is an hour long each file the difference (~5MB according to your report) becomes a bit more noticeable.