Your xpath syntax is wrong – you don’t need the inner set of square brackets – but even if you fix this:
//button[@type, 'submit' and text()='New']
it won’t select what you want it to. The problem is that the “New” is not text contained directly in the button element but is inside a child span element. If instead of text() you just use . then you can check the whole string value of the element (the concatenation of all descendant text nodes at whatever level)
//button[@type="submit" and contains(., 'New')]
Or check span instead of text():
//button[@type="submit" and span='New']
(submit buttons containing a span whose value is “New”)