Is is possible to use a ntfs usb disk as a liveusb with Startup Disk Creator?

https://help.ubuntu.com/community/Installation/FromUSBStick currently does not mention "NTFS" anywhere. So I'm guessing the support has been removed.

I just tried using Rufus 2.18, Ubuntu 18.04 Desktop 64bit, and SanDisk 64 GB and it failed to boot using NTFS (i.e. drops to Grub rescue shell). It works well with FAT32 as always.

Yes, it's possible to create a live usb with the NTFS file system to install Ubuntu, according to this article at Ubuntu Documentation, you can also use a FAT32 / FAT 16 file system.

Be sure to carefully read the article and follow the instructions step-by-step, because I tried the same with USB Stick (with the NTFS file system) and It worked correctly.