Qualitative research makes an attempt to map perceptions and opinions around certain topics in depth and in fine detail. Structured interviews do not lend themselves to this because you cannot ask further questions on certain statements and it is much more difficult to ascertain the meaning attributed to statements by participants. If it then has to be extracted, the chance of social desirability seems even greater and the chance of drop-out or half-full interviews also seems to me to be high. In terms of analysis, only a content analysis seems appropriate, but I am afraid you cannot gather that much relevant information on the basis of a few sentences.

Although less common, structured questions can be asked qualitatively as long as the questions are open-ended. You can also use your structured questions as open-ended questions in narrative interviews.

It's certainly possible, although what you're describing isn't anything I would call an "interview" if there's a) no personal interaction and b) no chance to ask follow-up questions, probe for more detail (to me: at least one those elements should always be present, ideally both.)

However, this could be a great way to generate qualitative data which could be analyzed essentially as text. Just as an example, in a project on "experiences of freedom in prison" (more or less) we conducted interviews with several prisoners, but were not able to arrange any meetings with women in prison. However, I was able to ask a group of incarcerated women (who I knew from a previous project) if they had anything to contribute, and they wrote several letters/short texts which both answered my (very general and open ended) questions and included a lot of additional comments, explorations, etc. The data was very different than that from the interviews, but was still very useful particularly in that they included a lot more personal reflective detail than most interview participants, since they had more time to sit down and think about it. (Of course, in an online situation that might also not always be the case!)

If your goal is to get more open-ended responses, this COULD be a good tool, with the proper promptings/questions, but it would be very important to consider if you are using it for its strengths (i.e. giving the respondents time to think about their answers, allowing a bit more creativity or artistic freedom) or simply for its "econimicalness" i.e. trying to get data quickly and cheaply within needing to conduct interviews (or needing the relevant skills to do that well.)

*In case you're looking for some "methodological support": there has been a long-tradition in Polish sociology, at least, going back to Florian Znaniecki of using "writing competitions" to generate (auto)biographical data. Essentially, sociologists would sponsor real competitions, where the 'best' written responses (to prompts such as - tell me about your life as a miner / the wife of miner) would win a prize, but the purpose was really just to get the data which could be analyzed - usually the 'best' contributions were the least useful for analysis.

See: Anna Kacperczyk (2020). Revealing the Silenced Spots: The Influence of Thomas and Znaniecki on the Study of Marginalized Aspects of Social Life. QSR, 16(4): 212-247.

I marked one answer as the best; however, this was an oversight. My apologies for Jürgen Magerman.

The three answers presented here are very useful and open a possible research avenue for those interested in qualitative research. My sincere thanks to Mariatha Yazbek, Aaron Bielejewski and Jürgen Magerman. Up until the next opportunity.