ELI5: They say shallow breathers don't use diaphragm. How is this even possible? Or even shallow breathers have to use diaphragm to certain degree?

I'm trying to understand deep breathing (Diaphragmatic breathing)
And is it even possible to breathe without diaphragm? Or even shallow breathers use diaphragm? Just not efficient as deep breathers?
And is it possible to strengthen diaphragm like other muscles?