I enjoy reading novels (fictional) – Crime, Thriller, Psychological.
I do read Islamic books too. I have been told that reading fictional novels is a waste of time and when we have been told to increase knowledge these books do not help us in any way. It is a stress reliever for me at times.
Is considered a waste of time to read such novels?

If reading these novels is purposeful then it’s not a waste of time. If you are reading them because it’s a way for you to relieve your stress that’s fine. But if it’s just for entertainment and fun then yes it would be a waste of time. My recommendation is to read less of such novels and add more quality to your reading, but if reading such novels helps you with stress then feel to read them (but to a minimum level).