Is it wise to stand up and respond to the Imam during the khutbah if he utters something that contradicts the creed or the Sharia, and is there a fear of falling into hypocrisy or fitna by doing so?

Speaking with the Khatib (preacher) during the sermon is permissible out of necessity and for a benefit. However, if refuting something that occurred in his sermon leads to discord or disturbance, then it is not legislated to address it, in order to avert corruption. It is more appropriate to advise him after the sermon with gentleness and kindness, and to clarify the ruling of the issue in which he erred, using the words of the people of knowledge, and explaining that returning to the truth is not a defect. If he responds, then all praise is due to Allah. Otherwise, the person should clarify the truth in a way that does not result in a greater corruption, striving for sincerity towards Allah.