> that's why I never prepare for interview above studying the actual company

You and me both. I just read a bit about the company before applying for the job. In the interview, I ask the interviewer only two questions: what’s the management style? Is it a servant leadership style with autonomous work, or is it a hierarchical task-based one? The second question is, what does an average day-to-day job look like? Sure, there are few stressful days and others are relaxed, but on average you can tell. Is it chaotic, always running against deadlines and having new tasks thrown at you, or is everything sorted out properly? Sometimes, I also ask about the meetings. I personally don’t like useless meetings. A lot of middle management uses meetings as part of the power dynamics and exerting power rather than actually discussing and solving issues.

Of course I would also want the information from your second question, but it never occurred to me that asking directly would get me that information. I guess if it's a leaf node they might just tell you the truth, but in general you'd expect the interviewer to say what they think you want to hear wouldn't you?

> I'd rather be rejected than got job I'm not qualified to do

As many people have pointed out, the interview process has diverged from real-world, day-to-day tasks you would be expected to accomplish once you get the job. Not actually being able to do a leetcode test (either due to lacking knowledge or interview stress) might not have any reflection on someones ability to succeed in the role they are interviewing for. How many people are dealing with sorting algorithms or traversing binary trees without access to the internet as part of their job?

It's a 100% unethical and flagrant cheating.

It's no different than if you had a much more technically competent friend off-screen feeding you the answers.