I feel that in Act 4 there is little opportunity to feel any sympathy for Macbeth, unlike in Act 5 where there is some possibility that you can see him as a man who appreciates he has wasted his life and thrown away opportunities. In Act four he abuses his power as king to destroy the family and home of MacDuff. This action goes far beyond the warning the witches gave him to "beware MAcDuff."
Of course, we may feel some sympathy for him in the way that the witches are deliberately giving him half truths and are pulling him away from the right track. But he is still ultimately responsible for his actions, and his actions are completely wrong. It is also notable that he now takes decisions without consulting his wife first, he has become a 'monster' and is not the figure who contemplates his actions that we meet in Act 5.
So very simply, in this scene where we see less of Macbeth and a lot of the consequences of his actions and the misery he is causing, we can have little or no sympathy for him.
In the first scene of Act IV, the reader might feel some sympathy for Macbeth since he is clearly plagued by fears of being removed from power. This is shown through his visit to the witches in which he reveals some details about the state of his mind. He talks about his "pale-hearted fear," for example, and is visibly moved and frightened by the apparitions, especially of Banquo.
But as Act IV progresses, any sympathy for Macbeth quickly disintegrates. In Scene II, for instance, Macbeth sends his henchmen to the Macduff castle. They brutally murder Macduff's son and the scene closes as these men pursue Lady Macduff. These extreme acts of violence leave the reader in no doubt of Macbeth's thirst for blood and of his overwhelming desire for power, even if it means killing innocent people.