Don't get me wrong - CT is a super handy thing to learn, and it pops up a ton when thinking about any software, including type checkers and compilers, but the OP was specifically asking about type theory and programming language implementation. Yes, you can express lots of category theory in terms of type theory (the dream is to implement all of it in terms of TT so that we can mechanise it), but it won't be the best use of your time if you want to build a type system.
I probably phrased my suggestion wrong. Yes, it's not central to OP's enquiry. But I did find a basic understanding of CT to help a lot when reasoning about types, and that lecture series gives just that in a relatively simple way.
