@ali_hugo It might depend on the question, but I would tend to prefer the first option - any open form question that is mandatory is likely to require more time (and thus give us less answers overall if people stop filling it by lack of time/energy). It might also be harder to interpet.
Imho when we need many open form questions, especially mandatory ones, it means we need more upfront interviews (which are an easier way to give open form responses for the interviewees, and show more respect for the interviewee than an “automated interviewer” via a form). The “free” responses obtained in the interviews then help designing specific questions, that we can validate against a larger panel of people via a form with yes/no answers.