Adding a bit of C to your tool belt will give you success wherever you go. The concepts it teaches are invaluable in understanding why things are built the way they are today. Everything from memory management, to trying to solve all these vulnerabilities, to why new languages have these crazy constructs.
Unlike Rust, Nim has far fewer learning resources (tutorials, books, courses) which may or not be important to you.
Recently I've been coming across ML family of languages. I see compiler books in OCaml. Atleast in the academic discussions I see the need to get away from C in terms of building reliable computer systems. Maybe it's a bit of a stretch to call it a systems programming language but maybe something to consider.
Python- it has a very simple syntax and it’s easy to learn. It can be used for modular programming and object oriented and it is forgiving if you don’t strictly follow the best practices. Therefore it can help to make thing working while you’re learning
I think C is pretty friendly as long as you can get through the basics of arrays and pointers. It's friendly in the sense that there is not a lot of grammar to learn.
But each field of system programming requires a deep understanding of something other than the language itself so overall I'd say it's difficult to get in.