Problem scenario
You are using Ubuntu with a desktop GUI. You want to create a USB stick with an .iso file to install Linux on some hardware elsewhere. What should you do?
Solution
Remove USB sticks from your computer that will not get the ISO. Why? You may accidentally overwrite one of them.
From the GUI desktop go to the Menu and search for "USB." You may find "USB Image Writer" or "Startup Disk Creator". It is fairly self-explanatory how to use "Startup Disk Creator."
If you want information on how to use "USB Image Writer," see this: https://linuxmint-installation-guide.readthedocs.io/en/latest/burn.html