Macbook mirror display shortcut (touchbar)

Hi community, I have a 2017 macbook pro (the one with the touchbar), its screen just recently went black out of nowhere, despite not showing any signs of damage or slowing down. I went to the largest official apple reseller here in Mexico for repairs but they just couldn’t do it without replacing the screen. They told me that the computer was still working and could still be used normally if plugged into an external monitor. When I plug it into the monitor it only shows my lock screen and nothing else, I now there is a keyboard shortcut to mirror the display (command + F1), but as my macbook is a touchbar model you have to press fn to show the function buttons, when I press fn the function buttons do show on the touchbar but the mirror display shortcut just won’t activate, the folks at the repair shop told me that this would work if I plugged in an external keyboard. Any recommendations on how to activate this shortcut (while the macbook is locked)? If I were to buy an external keyboard, will any brand work? Or does it have to be an apple keyboard?