The article is based on the following Windows 20 20H2 ISO (20H2 Build starts with 19042.nnn) that I downloaded from Microsoft: Your files, apps, and settings can’t be kept because your current version of Windows might be installed in an unsupported directory or you’re trying to install an older version of Windows. The dialog has a note at the bottom, which reads:
The options “Keep personal files and apps” and “Keep personal files only” are dimmed out, and “Nothing” is the only (default) choice.