Chosen Solution

I downloaded the latest version of Windows 10 ISO from Microsoft website and used boot camp assistant to create a bootable USB. When I clicked the continue button, a colorful circle spinning on the screen and it was stuck. It is macOS Mojave 10.14.4

A colorful circle spinning on the screen,it means it was running on your Mac, If it takes more than an hour, you are advised to give it up,i haven’t used Boot Camp for creating Windows 10 install USB,i can’t even tell if it’s good at this. Share another method with you if you want to try: https://www.uubyte.com/create-bootable-u