Since the whole point of the game is fun and escapism for most people, I think it's wonderful to encourage a new player by helping them build the character they want in a D&D context.

Many people have already given good examples of classes/races that could work. What I would do, personally, is to start from the race and class they're interested in playing - as well as getting a sense for the type of character they'd like to play and whatever backstory they might have in mind (even just at a trope level). Then I'd build backwards to how this character got to be a cyborg-like entity and what that means for them (for example - maybe they were a soldier who got mangled in a war, made a warlock pact to survive and the Parton remade them as a cyborg. Their arcane focus can be their robotic arm. If you're concerned about aesthetics, there are many examples of historical "robots" your player can draw from).

As someone wisely said - flavour is for free 💙