[expr.prim.lambda.closure] p3 says

The closure type for a lambda-expression has a public inline function call operator (for a non-generic lambda) or function call operator template (for a generic lambda) ([over.call]) whose parameters and return type are described by the lambda-expression's parameter-declaration-clause and trailing-return-type respectively, and whose template-parameter-list consists of the specified template-parameter-list, if any.

we just mention the case where trailing-return-type is omitted in [expr.prim.lambda.general] p5

If the lambda-declarator does not include a trailing-return-type, the lambda return type is auto,

we didn't explicitly associate the return type of the function call operator(template) of a lambda with the lambda return type. we merely defined the return type of the function call operator(template) as determined from the trailing-return-type.

I think we should change [expr.prim.lambda.general] p5 to

If the lambda-declarator does not include a trailing-return-type, it is as if its trailing-return-type is ->auto.

I also think saying lambda return type does not make sense. Since a lambda expression is a prvalue of a closure type and only the function call operator(template) of its closure type has a return type.