P1064 “Allowing Virtual Function Calls in Constant Expressions,”
adopted for C++20, permits you to mark virtual functions as constexpr and
then call them at compile-time. In fact, you can even mark them consteval
(also a C++20 feature), which means you can call them only at compile-time.
Thus (Godbolt):

Authored by Arthur O'Dwyer, Quuxplusone offers  explorations of C++ programming language features, standard library design, and modern C++ development practices. Readers can delve into advanced topics such as template metaprogramming, design patterns, and effective use of language features. Additionally, they can learn about best practices for writing efficient and maintainable C++ code, optimizing performance, and leveraging the latest language standards.

Arthur O'Dwyer

MSVC's experimental flag `/experimental:constevalVfuncNoVtable` omits the vtable for classes whose virtual functions are all `consteval`, but this produces non-conforming behavior. Under this mode, types with virtual methods are incorrectly reported as non-polymorphic, `sizeof` changes, and `typeid` returns the wrong dynamic type at runtime. The post explains why giving a class two different layouts is impossible, why omitting the vptr breaks type traits and RTTI, and concludes that the conforming alternative is `/experimental:constevalVfuncVtable`, which matches GCC and Clang behavior.

MSVC’s /experimental:constevalVfuncNoVtable is non-conforming