The C language itself is _beautiful_ but I am missing a beautiful standard library! Things which are trivial one-liners in other languages are sometimes 10-20 lines of brittle boilerplate code in C. If the standard library would have a bit more batteries included it would make trivial task easier and I could concentrate on actually getting work done. Opening a file and doing some text processing take usually a few lines in Python/PHP but in C you have 3 screens of funky code which will explode if something unforseen happens.
And working with additional libraries also a nightmare compared to composer/cargo. Adding a new library (and keeping all your libraries up to date) is dead-simple in basically any language besides C/C++.
tldr: I love the language itself but the tooling around it sucks.