The first round was a video call interview. This was terrible, they canceled the interview 30 minutes before without any reason, I had no idea what happened, they didn’t even send an explanation about this

The whole process is non-standard and quite unprofessional. I put "very difficult" just because there is not much one can do to prepare for such interviews. The questions were quite easy once you realize what they are looking for. Unlike large companies the recruiter doesn't have much idea about the interview process. The salary is not negotiated until the end of the process. They give you a take-home task which takes a few hours to complete and a panel discussion on that. Before that there is a round of "technical" interview.