Fully disable MacBook Pro's Touch Bar
You can tinker with the Keyboard Settings to get something close to your desired behavior. Here's one idea:

Set "Touch Bar shows" to "Expanded Control Strip" and remove all buttons on the Control Strip using "Customize Touch Bar...". Then set "Press Fn key to" to "Show App Controls".

Now your Touch Bar will be empty unless you press fn to show the App Controls.

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I also outline some ways to use Better Touch Tool to temporarily disable the Touch Bar in my answer on a related question.