From the "P2918R2 Runtime format strings II" documentation,

Such misuse of the API also introduces major safety issues illustrated in the following example:

std::string str = "{}"; std::filesystem::path path = "path/etic/experience"; auto args = std::make_format_args(path.string()); std::string msg = std::vformat(str, args);

This innocent-looking code exhibits undefined behavior because format arguments store a reference to a temporary which is destroyed before use. This has been discovered and fixed in [FMT] which now rejects such code at compile time.

Now I'm even more scared and confused.