Multiple parts of the standard indicate that deduction guide cannot have an explicit-specifier but can only have an explicit keyword preceding it.
explicitopt template-name ( parameter-declaration-clause ) -> simple-template-id ;
note that the standard says : explicitopt and not explicit-specifier.
or in dcl.fct.spec
An explicit-specifier shall be used only in the declaration of a constructor or conversion function within its class definition; ...
but the standard also says in over.match.class.deduct
If the function or function template was generated from a constructor or deduction-guide that had an explicit-specifier, each such notional constructor is considered to have that same explicit-specifier.
this quote implies that deduction-guides can have an explicit-specifier.
I do not see any particular reason why deduction guide couldn't have a explicit-specifier.
Is the issue in my understanding of the standard or in the standard itself ?
Can Deduction Guide have an explicit(bool) specifier ?