Been using Kotlin for 3, 4 yrs now. I recently took “Kotlin for Java Developers” on Coursera, and it was very interesting and there were a lot to learn. Wonder if there are more courses like this. I’m looking for a course for more experienced user, because the Coursera course took me 2 days to complete it. (and although I learned a lot there were lots of things I already knew.) Or a book like effective java of java. Any recommendations are welcome! Thanks.

There's Effective Kotlin by @marcinmoskala Highly recommended. My team and I also went through his advanced Kotlin course which gave a deeper understanding of Kotlin concepts.

That’s awesome! I’ll check that book. thank you for sharing your experience 👍