2019 MacBook Pro keyboard cleaning
How do I lock the keys on a 2019 MacBook Pro computer so I can clean the keys? Simply shutting down the computer doesn't work. When I push any key, the computer boots back on.
Boot into Startup Manager (hold option at startup. Then it wants a Mouse click to proceed.
How to clean the keyboard of your MacBook or MacBook Pro - Apple Support
If you use "canned air" DO NOT invert the can of Air -- unbelievably cold bad stuff will spray out and damage your Mac.