@BentiGorlich
It's a bit weird, it looks like the output of fdisk -l /dev/sdg indicates that your SD card is formatted with an HPFS/NTFS/exFAT file system, which is not the typical format for camera SD cards. Camera SD cards are usually formatted as FAT32 or exFAT.
I recommend that you backup everything on that sd card and reformat it to exfat or fat32 yourself on a linux system.