In short, before any formatting (outside of Windows10), of your SDXC card, please try this one, should help (I guess):
Afterwards just go back to GParted (if not used something within CLI).
EDIT: Of course you’ll need to create new partition table, and new partition(s), before any chosen formatting of this brand new partition(s). And also, sorry that I forgot what is not self-explanatory, please sudo umount /dev/sdb1, when SDXC card inserted within Librem 5 / before executing above command.