Complex sentence: Although exFAT is now widely supported in consumer electronic devices and Mac OS X, initially these could only handle FAT12/FAT16/FAT32, which formerly rendered exFAT (and flash memory formatted with it) impractical as a universal exchange format.
Split into simpler sentences: Although exFAT is now widely supported in consumer electronic devices and Mac OS X, initially these could only handle FAT12, FAT16, and FAT32. The situation had formerly rendered exFAT, and flash memory formatted with it, impractical as a universal exchange format.