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some people use Shift Lock (which is barely used, and closer to pinky), and a colleague of mine use the sequence 'ii'

Did you mean Caps Lock? Which tool do you use? I found https://github.com/susam/uncap but it does not have a MacOS binary.

You don't need any external program. Open System Preferences, go to Keyboard and click on "Modifiers Keys...", then you can map Caps Lock to Esc.