Thank you for your answer and advice! In pure mathematics - I found most interesting topics around algebraic topology. Next year, I plan to look into homology.

Thank you for your answer and advice! In pure mathematics - I found most interesting topics around algebraic topology. Next year, I plan to look into homology. These fields also have computational aspect and some applicability outside of pure maths: computational homology and Topological Data Analysis. This autumn, I finally looked a bit into category theory (applied) using this good book: https://www.amazon.com/Invitation-Applied-Category-Theory-Compositionality/dp/1108711820 https://www.amazon.com/Invitation-Applied-Category-Theory-Co..., and, unsurprisingly, found it exciting. Regarding PhD in an applied area: I tend to agree with you, and also keep thinking about focusing more on computational / applied mathematics so that my studies could be somehow related to my work. My tech focus at work is around data processing: with interest in distributed databases and computations. Heh, I see that distributed systems, algebra, topology, and categories are similar in mental representation in my head, they cause same kind of excitement when I study them: visualising, analysing, and playing with the systems of structures, connections, defined rules and operations :)