Why am I unable to delete a section from my Microsoft Forms form?

Check the response settings: Make sure that the response to the section you are trying to delete has been discarded or deleted and not kept for future review.
Change the question type: You can set the question type to none, if the question no longer needs to be answered.
Review the quiz conditions: Check if there are any conditions set for the quiz questions in the deleted section.
Adjust the page settings: You can change the page settings to hide the section and ensure that the questions can no longer be answered.
Review the form template: If you have based the form from a template, try to delete the template and recreate the form from scratch.