The requirements are classic Power Platform ALM requirements:

the custom connector must be deployed consistently across environments

it should be editable only in development

The correct design choice is to add the custom connector to Solution1 .

Why B is correct:

Putting the custom connector inside the solution makes it part of the ALM package

It can then be exported and imported consistently across environments

In production, when deployed properly through managed solutions, it is not freely edited there, which supports the requirement that editing happens only in development

Why the other options are not correct:

A. Share the custom connector controls access, not ALM packaging and deployment consistency

C. Create the custom connector in the default solution is not the recommended ALM approach for controlled deployment

D. Add the custom connector to GitHub may help source control, but by itself it does not satisfy Power Platform deployment packaging across environments