I hear this all the time on HN. I am nearly a neckbeard at this point as a programmer. I have never once used any linear algebra in my career. Discrete math: Only a tiny bit, and mostly to pass HackerRank/LeetCode questions for interviews. Looking back, the highest impact (to me) undergraduate comp-sci course was intro to algorithms. You really use those over and over again, even if you are just "using the library" (vector/map/etc.). It helps to know what and how they do it, even if you cannot write it from scratch yourself.