#include <format>

int main()
{
    volatile int vol = 42;
    auto ret = std::format("{}", vol);
}

error C2668: 'std::_Format_arg_traits<_Context>::_Phony_basic_format_arg_constructor': ambiguous call to overloaded function

The same code compiles fine with {fmt}.
MSVS 17.0.4

Update:
It's rather volatile integral types fail to compile, because volatile double and float compile fine.