C is still widely used. I think if you really want to just work with C you should focus on embedded stuff, surely not every job in embedded requires experience.
One industry which is quite C heavy is aerospace. You do not need to work for Boeing/Airbus though, there are many, many suppliers who are doing embedded work.
We are mostly using C++. C skills do come in handy for the existing body of software in systems such as Linux, but we very rarely write new code in C.
I would absolutely hate working in embedded (if it runs linux it's not the kind of embedded I'm talking about) for a salary. Nobody treats C with any care or respect in those areas. Either that or the language is written like a legal document. If you like C because you've played around with it, understand the abstract machine and can write it safely working with a modern standard, don't expect embedded development to be ANYTHING like that.
Anybody who is interested in learning/using C/C++ SHOULD absolutely look into Embedded Programming. That is where the "rubber meets the road" and gives you the intellectual satisfaction of learning/understanding "everything" (i.e. HW & SW). Embedded Development encompasses a broad spectrum from Application programming (eg. Apps in a Network WiFi Router), Kernel/Device Driver programming (eg. RTOS/Linux in the same Network WiFi Router) to bare-metal programming (eg. 8-bit etc. MCUs). So one really gets to know how to use C/C++ (the Good, the Bad and the Ugly) as the situation demands to solve a problem. All the standards are merely guides to follow (i.e. not commandments from above) which is only deviated from when needed.