I haven't completed the first day at my new job. We had an onboarding call where the HRBP (Human Resource Business Partner) was very rude to me. My intuition says that I will be treated the same way throughout the job. I have not yet finished my onboarding formalities, should I quit now?
You should absolutely not quit now, that's ridiculous. There is one person who you perceived as rude (which doesn't mean necessarily they were rude), and that is quite irrelevant to your job 99.9% of the time. You will run into lots of people including your future colleagues who have problems with people they don't know, and after a week or two of knowing you they are the best colleagues to have.
There is a reason why you have three months of probation and not one day.
I found this link that seems helpful:
Everyone has a bad day, sometimes. I wouldn't jump ship only because one person (not even your manager) is rude at day one. Give it some time and get a feel for the company culture.
Your team and your direct manager will be much more important to you than some HR person. Most of the people in my company don't have any contact to HR for years. Don't overthink this.
Let this go
In the course of a normal job, you will hardly interact with HR at all. What matters is how you are treated by your team, your boss, and your customers. HR is none of those. I can't think of any company I have worked for where HR set the tone for a company, though at one they thought they did.
Further, if you quit every job where someone is rude to you, all that will happen is you spend a lot of time looking for work.