MSVC accepts lambda with deleted parameterized ctor while GCC and Clang rejects

The program is ill-formed and msvc is wrong to accept it because any construct designating the deleted function (except to declare/define or reflect it) is ill-formed as per dcl.fct.def.delete:

A construct that designates a deleted function implicitly or explicitly, other than to declare it or to appear as the operand of a reflect-expression ([expr.reflect]), is ill-formed.

And since the use of C(3) in [b = C(3)] is neither declaring the deleted ctor nor an operand of a reflect-expression, the program is ill-formed.

Also, the declaration of var2 is accepted by all compilers because [C(3)] is an int capture and is actually equivalent to writing [C=3].