These don’t need to be 3 different questions. The vocabulary (knowing what pre, in, post means) is nice, and the questions follows what I see as the “typical” recursive tree-problem skeleton.

The first one is how I think it should be solved (albeit recursively). If memory serves, doing it iteratively for infix is a bit interesting. The other two example solutions are very terse.

class Solution:
    def preorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if root is None: return []
        prefix = self.preorderTraversal(root.left)
        suffix = self.preorderTraversal(root.right)
        return [root.val] + prefix + suffix

class Solution:
    def inorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if root is None:
            return []
        return self.inorderTraversal(root.left) + [root.val] + self.inorderTraversal(root.right)V

class Solution:
    def postorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if root is None: return []
        return self.postorderTraversal(root.left) + self.postorderTraversal(root.right) + [root.val]