I would say it is effectively a big waste of time. They are obviously not hiring nor growing so to get the role you will need some stars to align and also you will need to completely crush all of the interviews however since they dont give feedback it is hard to know exactly why they reject.
It does not matter if interviewer are neutral nice to you if there is very little respect for your time, so if you are actually thinking about joining Brex I would dissuade you a bit, not because I dont think it is impossible or that it is a bad company to work for but rather because the odds are more prone to be a time sink, if you are interviewing in multiple places I would put more focus on the other processes.
For instance the debugging round, It is not hard to find all 4 bugs, but miss one and it is over, your whole loop can easily be casted aside by trivialities.
In system design be prepared to be interrupted constantly by questions until you are not able to answer them, you need to know your basics really well and your answers need to be swift, understanding the logic is not enough interviewer want names, This is the hardes interview, as you the interviewer is there to antagonize you, they are looking for a reson to discard you, dont give them any, if you mention something be absolute confident you know everything about it.
AI interview is not transparent, you will never know what you need to do aside of basic requirements. Quite honestly it a very silly interview.
Overall if you have the opportunity and the time then do try the process, but for most people interviewing it is going to be a rejection with no feedabck and a very long process, lower your expectations and focus on other processes if possible.
