The "Check for updates" button often doesn't show any immediate feedback, especially on stable builds. It silently checks in the background and only notifies you if something new is available (via notification or in the list).
To confirm it's doing anything:
Tap it once, wait 30-60 seconds.
Go to Settings > System > System update > see if it says "Checking..." briefly or shows "Up to date" after.
Or check logcat via adb (adb logcat | grep Update) right after tapping – you'll see lines about checking servers if it's active.
If nothing at all happens even after waiting/reboot, it could be a connectivity glitch or rare UI bug. Try toggling airplane mode or Wi-Fi off/on before checking again. Works normally for most people once you know it doesn't flash a spinner or toast.