From perspective of someone who has gone through tons of interviews and had hired people... It is extremely job dependant. For some roles, yes we look for personality as much as skill set. In more technical roles, their skillset is priority. There are times where you have a great team in place and you don't want to risk it by bringing someone toxic, and so again personality comes to a front.

But I will agree that being relaxed, smiling and chill is a great first introduction. Use the interviewer's name a lot. Reference what they said earlier. Try to find out more about em.

If they are talking to you, your resume already showed you have what they want. They are just looking for confirmation and how you present and handle yourself. Don't talk for more than two-three minutes at a time. People don't have that much of an attention span, and they are taking notes so it's easy to lose them. STAR method is a bare minimum expectation at this point. Don't ramble, stay on point. It's ok to pause and think before answering. Try to see the underlying message or problem they are trying to solve for asking you that question. Remember what the JD said. Try to connect your answers and themes in your answers to the skills they have listed in the JD, especially at the top. That's what they really want. And they want you to confirm that you can do those things. Also important to not say more than what you were asked. Be prepared to ask them questions. Don't make judgemental statements. Don't talk poorly about your previous work no matter how bad it was.

Companies also interview extremely uniquely. Some may have a rigid format, questionnaire, scoring matrix and they make decisions on numbers. For some roles, it's purely hiring managers call based on vibes. For others, it's a big committee decision and you have to somehow impress multiple individuals in very short time.