I put a new 128GB micro SD card in my Fairphone 2 which came exFAT formatted and let (in this case) LineageOS use it as external storage. No problem there.
But in TWRP 3.2.1-0, I couldn’t mount the card. The card was there to mount, but every try to mount it failed.
I checked the card I used before and it was FAT32 formatted, which for compatibility in general makes sense to me. I guess back then Android 5 formatted it that way.
Since I feel more comfortable granting compatibility to things, I reformatted the card to FAT32 and TWRP happily mounted it.
(Since newer Windows versions don’t like to format things in FAT32, there’s guiformat, which worked for me, but you can do it with diskpart, too.)
But since I am curious and did find nothing much about it:
Does anybody here know whether in principle an exFAT card should work in TWRP or not?