By design, the Request Response option will only prompt the respondent to answer a question if left blank; it will not force an answer.
FWIW, it's been a few years since I tried to use the Table of Contents feature, but I thought it was meant to allow respondents to jump between different blocks of the survey using its navigation (not by using the Next button). Maybe that's changed or my memory is faulty, but what I do remember clearly is that the TOC feature was very unreliable and I had to abandon the idea of using it for my projects. The navigation was not intuitive for respondents and other features that I needed to use (like response summaries) were basically incompatible with TOC. When I shared the challenges with Qualtrics support, they told me that the TOC was not on the product roadmap and we shouldn't expect to see it developed or supported much more. This was about 5 years ago, so I'm surprised it's still available.

MatthewM yes I don't want to force the response but, how could I let the respondent know which questions are unanswered at end of survey.

https://community.qualtrics.com/XMcommunity/discussion/comment/54529#Comment_54529I believe the TOC will show the status of each block, but there is not an out of the box solution to show the exact questions that are unanswered. You would have to set up something for each question, like using Display Logic to show a text object on the last page for each question that was not answered. This would be easier for short surveys, but less feasible the longer the survey is.

MatthewM yes, TOC shows the block is incomplete at end of survey if it is untouched. But, if the block is touched without answering Request Response questions it is marked as completed.

YBAIRA it has been a few years since I used the TOC but I recall having the same issue as you. I ended up having to use response validation to make sure the answers I wanted answered actually were before accepting submission.
I believe I achieved this by adding another page/block. In that block I had questions that corresponded to each TOC section. It was a text/graphic question. And I put validation on those questions. If when they submitted there was an error then I could put a general message about what block to go back to and which questions to make sure were completed in that block.
It was the only way I could figure out how to do it and allow bouncing between blocks because, as you point out, force response won't let you leave a page until the condition is satisfied. Thereby blocking the bouncing between sections in the TOC.
Now I might be able to write Javascript that is more fancy than my solution from years ago but haven't had the need to do so.

Have you found the answer yet?

bstrahin thank you, that works. I have over 200 questions with Text Entry, Side by side, form field and Multiple Choice questions. Looks like I need to put lot of validations and put a general message.