[MS Windows System Backup] One of the volumes specified for backup is invalid because it is either not on a fixed drive, is not formatted NTFS/ReFS, or is read-only.
As the error says, one of the volumes is probably FAT32.
You can try converting the FAT32 volume to NTFS or removing it from the backup source.
Don’t convert a volume to NTFS if it needs to be in FAT32 format for Windows to boot.
Don’t remove a volume from the backup source if it is required for the system to boot following a disaster recovery.