I have interviewed here twice, and both times had a very similar and positive experience. They provide all the information you need to prepare, including the system design question.

They like to ask multi-part coding questions that build on top of one another. They are looking for code fluency, debugging skills, clean code, and code that compiles and runs, rather than the most optimal solution.

The questions aren't difficult as long as you know your basic data structures and object-oriented design in your language of choice. Personally, I'm not very good at finding the most optimal solution right away, but I'm pretty good at communicating, so these questions were not difficult for me. Since it's pair programming, the interviewer will help you out when needed. They don't care about the most optimal solution, but you should still be able to tell them the runtime and memory complexity.

For the behavioral interview, make sure you know how to talk about your past experience and projects well, and you will do fine.

My only complaint is that the recruiting turnaround time can take a while. The first time, they took three weeks from my onsite to tell me that they were extending an offer. By that time, I had already signed another offer. This time, I made sure to give them deadlines.

I think the technical bar at Square has gotten worse over the past couple of years, unfortunately. If you ever get the feeling that you're smarter than your interviewer...

The interviewers write their own questions, so it's not something you can study ahead of time.

Practice object-oriented design questions.

Nothing is harder than LeetCode Hard problems. It's usually LeetCode Easy for the first part, and LeetCode Medium at most for the subsequent parts.