The usual suspects are the keyboard support in Windows (enabling the extended keyboard navigation in MacOS made some apps act very strangely), and most of the look and feel of MacOS. There have even been things I really liked in ChromeOS.
Obviously there are many nice touches in the big Linux DEs, and I would rather be in KDE Plasma than anywhere else. Because of this, I'm generally not surprised when I encounter something that is done better than Windows or MacOS.
However...!
Yesterday I was editing filenames in the file browser, and accidentally navigated down to the next file in the folder - still in filename editing mode! It was a feature I didn't even know I wanted. Suddenly, I could edit a whole list of files, just as if it were rows in a text file. Now it's Monday, and I'm back in Windows. I am unlikely to need to use that feature, but still wish I didn't know what I was missing.