Why not boot macbook pro 2016?

Gulp, you mean you've had no backup all along?

Hold alt key at startup.

Or...

Shift key

Or...

1. Start up from macOS Recovery

To start up from macOS Recovery, turn on your Mac and immediately press and hold the following combinations on your keyboard.

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

Ouch, you'll have to have Apple take a look at it. :(