An engineer called, didn't introduce themselves, and started by nearly forcing me to disclose undisclosed information about my current job. There wasn't an ounce of politeness.

The interviewer then asked a seriously tough question of the type: "You know the answer already and can solve it pretty fast" or "You don't, and you'll struggle for an hour to break it down and desperately find a beginning of a solution".

The interviewer, in no way, helped me or gave me some kind of direction to explore. They barely spoke and finally asked me to solve an easier question.

At this point, I didn't have a lot of time left, and all I could think was, "I would never want to work with such a person. I am wasting my time."

I ran out of time, and the interviewer asked in the coldest of ways, "Do you have any questions?"

This was probably one of the worst interview experiences I have ever had.

Make sure you are very fresh with most linear algebra concepts.