Regex does the job for most business software, iostreams is alright, using them since 1993, std::format is cool provided one has control over their compiler version,...
Regex is absolutely not suitable for most use cases that I have come across. Iostreams formatting is awful, especially if you care about internationalization (which is very common).
Not sure what the issue with std::format would be here, you would have to elaborate. Obviously you need to specify a minimum version to have support for it at all.
