At least since C99, I've seen a trend where ISO tends to bring in unnecessary C++ features in. In fact, the current boss of WG14 quite explicitly calls for bridging gaps, modernising capabilities, and bringing select features (like constexpr object definitions and ergonomics) closer to what developers enjoy in C++, while "balancing C's unique philosophy and design constraints". I don't suppose it sat well with most C developers who feel C++ has evolved into a language of its own and that we shouldn't try to bridge gaps that don't exist. And consequently, the very fear of "dead on arrival" features have already crept in. Off the top of my mind, VLA is one such example. Appeared in C99 and is now a deprecated feature.
That said, C89 is, for most parts enough to express that largest chunk of your codebase. But sure, you might need a little bit of size guaranteed integers, so you could borrow that from C99. What're you left with? The convenience of declaring variables midway? That's about as far as it goes. In very rare circumstances you might want to statically assert macros is global variables. Sure, pick C11 just for that task.
If I really need some awesome syntax sugars, I'd rather use one of those modern languages like Zig, Rust and what nots..