I'm not a math guy but this seems a bit narrow. I don't know how you'd get a good general overview, because there are dozens or hundreds of mathematical fields, often with overlap, but I know calculus and ODEs and I wouldn't say I "know math" even remotely.
It seems like abstract algebra is a good starting place since people who do
"know math" seem to reference it a lot - set theory and number theory maybe? College-level geometry would probably be nice. Mathematical logic? Complex analysis?
I've learned some things in data structures, algorithms, numerical analysis, combinatorics, and computability theory, mostly as a result of reading about computer programming. That stuff is awesome to me but I don't even know how you'd get there from a "general mathematics" background. If you want computer math I recommend those topics though, I doubt you can do much with computers unless you have at least data structures, algorithms, and computability theory - but for "more discrete" tasks combinatorics is a must, and for "more continuous" tasks you really need numerical analysis. Might even want to study some more programming-related stuff too, knowing how floating-point types are implemented
would be awfully valuable if you ever want to do math-related code.