I enjoyed using Windows 7 a lot. It was stable; much more so than previous versions and actually later versions - an update wasn't likely to break support for any devices or introduce a regression like it sometimes does on 10/11.

KDE 5 gives me a similar feeling to what I had with Windows 7. It's very customisable, and indeed with some theming you can make it look almost identical to Windows 7. But what is particularly nice is not so much the aesthetics, but rather the depth of functionality and polish that KDE has. There are hardly any rough edges, and features like KDE Connect are conceptually simple but mind-blowingly efficient in practice.