The most important C feature that C++ lacked for a long time was C99 designated initializers, but C++ finally supports them in C++20[0].
Other than that... I'm not sure what hobbling you have in mind. Many C23 features come directly from earlier C++ standards (auto, attribute syntax, nullptr, binary literals, true/false keywords). VLAs? Though these are optional in newer C standards, too.
> C99 designated initializers, but C++ finally supports them in C++20
Unfortunately C++20 designated init has been butchered so much compared to the C99 that it is pretty much useless in practice except for the most trivial structs (for instance designators must appear in order of declaration, array item init is completely missing, designator chaining doesn't work ... and those are only the most important things).
