Which of the following constructor-related concepts is non-relevant in C++?

Copy constructor, conversion constructor, and overloaded constructor are all relevant constructor-related concepts in C++.

A copy constructor creates a new object as a copy of an existing object.

A conversion constructor allows an object to be created from a value of another type, enabling type conversion.

An overloaded constructor means a class can have multiple constructors with different parameter lists.

A virtual constructor is not supported in C++. Constructors are responsible for creating objects, so they cannot use virtual dispatch in the way virtual member functions do.

Therefore, the non-relevant constructor-related concept in C++ is virtual constructor.