Programming

This is going to sound fishy.

Recently getting into cybersecurity things and have been pretty interested in looking at malware and maybe making some myself to get the hang of it. Do you guys know any good repositories with malware to learn from? For example, if I wanted to make a credential stealing program, there's a lot of different programs that may have credentials that are valuable. Or, maybe writing a keylogger? I took a look at a rust crate that can record keystrokes but has kind of a weird (or at least not as easy) type system because of different OS implementations, but how do different types of malware consolidate those differences?

I guess the broader question I'm getting at specifically is looking at how already made programs get around different technical obstacles like detailed above.

Thanks