Feel so lost and behind on LC

Did about 100+ LC, but did 3Sum today for the first time. I had an idea of the converging two pointers and expected it to be similar to the two sum with sorted array. However getting rid of triplet duplicates was so tough, I don’t know in an interview if I’d get it perfectly. Or even the running solution for it. I had to consult AI for some help, as I also didn’t know lists weren’t hashable (or forgot, I might’ve encountered it before). I feel like i’m doing the whole thing wrong. Then i look at the solution and i’m not sure how i’m supposed to come up with it. Any advice?