What are the different ways to apply a constraint to a template?

You can constrain templates via: a concept name in place of typename (template <std::integral T>), a requires clause (template <class T> requires C<T>), a trailing requires clause after the function signature, or the abbreviated function template syntax using a concept with auto (void f(std::integral auto x)). All express the same kind of requirement.

void f(std::integral auto x);         // abbreviated
template <class T> requires C<T> void g(T);  // requires clause