I feel Rafe Spall is not convincing

For me, Rafe Spall's work in Just Mercy (2019) is easy to talk about after watching. Some emotions are too simple, and I cannot believe the character enough. The role needs more detail, but the performance stays on the surface. For me, it does not feel very real in many scenes. I do not hate it, but it did not pull me into the story. Many moments pass very fast, and I do not remember much after them. I remember both the good parts and the parts that did not work so well.