WoeUSB-ng for creating a Windows 10 USB Stick on Ubuntu 20.04
Download the latest ISO from here
https://www.microsoft.com/en-us/software-download/windows10ISO
Open your terminal, type these commands
sudo apt install git p7zip-full python3-pip python3-wxgtk4.0 grub2-common
sudo pip3 install WoeUSB-ng
https://github.com/WoeUSB/WoeUSB-ng
That's it now you can use a free USB stick to create a bootable stick. Just use ventoy instead IMHO it's much, much better
https://www.ventoy.net/en/index.html
On Windows I think you can use Rufus instead of this ghastly windows crap program