Canva Front End Software Engineer interview questions

The interview has 3 rounds. They will ask you some basic coding in the first round such as data structure. They recommend a book which is called you don't know JS yet, which is helpful.

4 rounds, 7 interviews including 6 technical ones and 1 value interview after completing all the interviews, I got one rejection email without any reason. The recruiter said he can discuss the feedback in the following week, but no any response since then. I am really confused what the criteria are as I solved all the problems in the interviews, and after preparing the interviews for several weeks, I feel it is a waste of time