But it is possible to run even the latest Xcode 26.6 by directly executing Xcode.app/Contents/MacOS/Xcode, and Xcode will run. This trick doesn't work with Xcode 27 anymore though. If you try that, you'll see a warning message that says something like "Xcode requires macOS 26 to run".
It does. The latest officially supported Xcode version runnable on Sequoia is 26.3. See https://developer.apple.com/xcode/system-requirements/
But it is possible to run even the latest Xcode 26.6 by directly executing Xcode.app/Contents/MacOS/Xcode, and Xcode will run. This trick doesn't work with Xcode 27 anymore though. If you try that, you'll see a warning message that says something like "Xcode requires macOS 26 to run".