I have configured Microsoft flow on a task list item creation using "Send Mail with Options". Different options that I have configured are "Approve" and "Deny". It is working fine however I wonder if there is a way to take user input (comments) as mandatory when user clicks on "Deny" option in mail.
recommend you to use normal "send e-mail" option, so you can embed a link to your task-item there can an approver post a comment and take action (Approve or Reject)
then you'll be able to add/embed approvers comment on mail body