The process consisted of a first call with the recruiter, a coding screening session and then a set of four other virtual/onsite interviews.
The technical interviews were the usual boring and pointless codility tests. On one hand they are not strict on getting everything right, which is good, but on the other hand these tests are close to be totally useless, so rather then removing them, they throw one more at you hoping that this would provide (self induced) "signals". On the architectural question: I'm not sure about the value of forcing someone to make final decisions in 10 mins on something that should be well thought and would require at least a couple of cycles to fully understand the requirements within the company. I'm sure they would claim that there is some super smart reason for that nobody can get, not even real psychologist and subject matter experts.
Anyways, I was rejected for lack of an unspecified experience/skill which, if I understand correctly, I was anyway capable of, but didn't bother to ask or investigate. No questions on real world experience, all of their questions could be answered by an unexperienced engineer with a bit of codility and youtube "training". I guess this is what they are actually looking for, despite the job title.
Overall, nice people, I enjoyed one interviewer especially, very friendly, helpful and transparent. I'm sure the company and the environment is good, but... their interview process isn't effective (I doubt this leads to good hiring decisions) and wasted my time, as they could have stopped me early on, or simply asked meaningful questions.