In the book series The School for Good and Evil, Sophie’s true love is implied to be Hort of Bloodbrook. Hort is a kind and gentle giant who is always there for Sophie, even when she doesn’t deserve it. He is also the only one who truly understands her, both her good and bad sides.
In the Netflix movie adaptation of The School for Good and Evil, Sophie’s true love is not explicitly stated, but it is hinted that it could be Agatha. Agatha is Sophie’s best friend and the two of them have a very strong bond. They are always there for each other, no matter what.
Ultimately, who Sophie’s true love is is up to the individual reader or viewer to decide. There is no right or wrong answer.