KeyboardCleanTool
KeyboardCleanTool locks your keyboard (including modifier keys and the Touch Bar) and optionally trackpad & mouse, so you can wipe them without producing any input.
Version 8 is a complete rewrite: it darkens all screens so smudges become visible, shows a status card with the elapsed time, prevents display sleep while you clean, and can unlock automatically after a timer. There is deliberately no keyboard shortcut to unlock — you unlock by pressing and holding a trackpad or mouse button for a few seconds.
Back in 2011 Apple rejected the app for the Mac App Store because apparently it's "not useful". More than a decade later I still use it every week — and I have heard of people who use it to let their toddlers pretend they work on a computer. Also people with cats.
Older Mac? Download the previous version
KeyboardCleanTool 7 is the previous, much simpler version (keyboard & Touch Bar lock only). It runs on macOS 10.11 up to macOS 12 and still works fine if you cannot update to version 8.
From the same developer: BetterTouchTool
KeyboardCleanTool is a free little side project of BetterTouchTool — the app that lets you completely customize your keyboard, trackpad, mouse and pretty much every other input device on your Mac. As a thank you for stopping by, here's 15% off:
Enter the code during checkout.