Is constrained auto cast valid?

Question

Since C++20, the constrained auto is introduced by:

Concept auto identifier = init

Which means, for instance:

std::integral auto x = 10;

is valid.

Also, for new-expressions, concept is allowed to be paired with auto:

new Concept auto { expr };
// or:
new Concept auto ( expr );

auto{expr} or auto(expr) was introduced in C++23 as roughly equivalent to:

auto __temp { expr };
return __temp;

Does it mean that Concept auto { expr } or Concept auto ( expr ) is also valid?

The simple use case would be usable in trying to create a decay copy while checking its operations checked by constraint.

Answer 1

[dcl.spec.auto.general]/5 allows only auto to be the simple-type-specifier of a functional type conversion, even though a constrained placeholder-type-specifier can be a simple-type-specifier grammatically.