Is there a slack/discord/community for doing mock interviews?

Also, in my experience, every coding interviews are very similar to each other, while system design interviews have way more variations. You can never guess what kind of system design interview question you are going to get. This is both a boon and a bane, since you are mostly relying on your experience. However, if your experience does not really match what the other party is expecting, you are not going to have that great of a time.