CSE is mainly concerned with the invention and development of new software and hardware.
IT is mainly concerned with the selection and use of already-available software and hardware.
Both CSE and IT entail research requirements analysis and design for purpose: but they ask different questions and use the results in different ways.
CSE asks: what new system as a collection of code and electronics can be designed and should be built? Would it be useful either immediately or in the future?
IT asks: what new system selected from catalogues of available code and electronics should be purchased and employed? And how should it be employed and people trained to use it?
CSE includes the study of how things work internally.
IT largely takes the internal workings for granted.
Both CSE and IT look outwards in much the same way studying how to provide systems for people to use efficiently or innovatively.
But when they look inwards they do so in very different ways.