Is a person considered an apostate if they watch a video that mocks religion and display something akin to a smile or a nod, without clearly recalling the intention behind the smile or the disavowal in their heart?

What was mentioned is not apostasy, and one must be cautious about listening to falsehoods unless it is with the intention of demonstrating their falsity, because being lenient in listening to them is a means to evil. You can refer to Fatwas no. 109383 and no. 146893 to understand the criteria for mockery that expels one from the religion and the causes of apostasy.