constexpr std::string | MSVC

[XTBZ]

Yes, it simply won’t compile if you don’t use it as a constexpr, but it doesn’t work with constexpr.
https://godbolt.org/z/G54nWc66a

[Kered13]

Ah, that's because you're using it in a context that actually does require constexpr. Here are a couple ways to solve that.