no, you can't change it, i am pretty sure it has to be either FAT32 or exFAT
it does have other loading modes if you explore the menu, one of them i think it copies the iso to memory and boots from there, and anyway, if it's linux, most linux live images are under 4gb so you can use FAT32, but either way, yes you can make other partitions, usually ventoy puts itself on a partition at the end of the disk, usually fat32 as this works on both BIOS and UEFI, and then it typically partitions the rest of the disk as exFAT but it can also be FAT32 and i think the only limitation is you need to have that as the first partition, you can make persistent storage on an ext4 partition on the remainder of the disk in between these two