When I started preparing for interviewing, I spent most of my times studying general data structures & algorithms and practicing applying them to different problems. I don't think this is so bad and can lead to a lot of learning you wouldn't do otherwise.
The frustrating thing, is how easy it is to hack the test. After one particular interview, I remember talking to a friend about how hard the technical interview was. He told me that he had already seen the problem and knew it would come up because he bought leetcode premium for the interview. Kind of frustrating to spend hours and hours learning data structures and algorithms when the real key to success is getting lucky and memorizing the problem before hand