Prevent my MacBook to turn on

Your description sounds like the computer is only sleeping, not turned off. There are several ways to turn off a Mac but the easiest is to use the "Shut Down..." command under your Apple menu:

use this article:

How to clean the keyboard of your MacBook or MacBook Pro - Apple Support

.

The 2018 MacBook Pro powers up when a key is pressed:

How to turn your Mac on or off - Apple Support

"Additionally, MacBook Pro (2018) and MacBook Air (Retina, 13-inch, 2018)

turn on when you press any key on the keyboard or press the trackpad."

I obviously have to get newer Macs! Thanks, Bob.

Me too. There are so many changes it is sometimes hard to keep up.

So, let me see if I understand you correctly: you've shut down your computer (by going to the Apple Menu and selecting ' shut down') but pressing any key turns it back on…?