https://enduringword.com/bible-commentary/1-samuel-28/

iv. Some believe that this was a genuine (but strange) appearance of Samuel. This is the best explanation because it is supported by the reaction of the medium, who got more than she bargained for. It is also supported by the truth of what Samuel said (and the text says that Samuel said it). Some may say that it is impossible for Samuel to reappear in some way, coming from the world beyond back to this world. But Moses and Elijah also came from the world beyond back to this world when they appeared with Jesus at the Transfiguration (Matthew 17:3).