To get a standard WIndows 10 or Windows 11 ISO is easy. For a latest public release ISO, just go to official Microsoft ISO download site, and download an ISO as told in this tutorial on our sister site Ten Forums:
https://www.tenforums.com/tutorials/9230-download-windows-10-iso-file.html
To get a Windows Insider ISO, see our Eleven Forum tutorial:
https://www.elevenforum.com/t/uup-dump-download-windows-insider-iso.344/
But, what to do if you want to modify your ISO? Add files, make installation unattended, add drivers, and so on. OK, many even quite senior geeks suggest you can use this or that third party tool to "burn" an ISO.
I am something you could call a Windows purist. I have never used, nor will I never use any third party...