Windows does not allow you to format cards bigger than 32GB to FAT32. But it seems to work with them if someone else formats it.
Also please note that AR12 officially does not support cards bigger than 32GB (I'm not sure whether a FAT32-formatted 64GB card will work, but you may want to try that provided you already have that card and that mixer). If you want a safe choice, get a 32GB card and you will be able to format it to FAT32 in Windows.
To format a 64GB SD card to FAT32 you need either a third-party formatting utility, or a friend with Mac or Linux. See https://www.raspberrypi.org/documentation/installation/sdxc_formatting.md
for more details.