I vote to stick with C for another reason, integration with other languages. If your project is a nice C library, it’s vastly easier for people using other languages, C, Python, whatever, to interface with your library rather than having to re-implement it.
C++ is imo an awful choice for a library because it ends up restricting this to other things written in C++ (unless of course you wrap it up in a C abi but that is messy).
I’d prefer a base in C with a C++ wrapper as required.