I totally agree with @WiIfred P that you can easily use the windows 10 media creation tool. And Run that tool and create your own iso file or usb device easily. But still if you want to create a bootable iso file from a bootable usb you can also do that easily. Just you have to follow some steps and the right software...
You can also follow this link for more information:
https://www.buildsometech.com/2019/09/convert-bootable-usb-to-iso-image-file.html
I hope this helps. Feel free to ask, if you face any problem and i will definitely revert back.
Thanks
Sanyam