The absolute basic mathematics that is required to understand basic ML/DL are calculus, linear algebra, probability and some convex optimisation. We are all aware of that.
But ML and DL has become a vast field both in breadth and depth. A single person can’t understand the field entirely. There are specialistions and sub-specialisations and further more.
If you work in a branch of ML/DL research where some other math fundamentals are needed to understand research papers and do innovative research, can you mention your field of work and the math fundamentals that are required to gain entry into your field?
Measurement theory, causal inference, Bayesian stats, the whole megillah.