There is so many way to create windows 10 bootable USB drive. But here is a simple and easy method.
first open given link for download tool.
open MediaCreationTool1909.exe and wait for analysing .
Wait for some moment and then click on accept option.
Wait some second or a minute to response.
Tick on create installation media(USB flash drive,DVD or ISO file) for another PC and click on next.
Unmark Use the recommended option for this PC.
Now you can modify system as your wish. And click on next.
Choose USB flash drive option and attach a pen drive or other drive to the PC. and click on next.
You can see your drive in a list then select and click on next. Process start wait for an hour. It depend on your network speed.
After complete remove your drive and you can use that drive as a usb bootable drive.