Every Player’s character has an object called an Animator, which allows developers to load and play their custom animations on. The Animator would usually be parented under the Humanoid object of the Player.
This method you are trying to call on the Humanoid object of the Player is not a valid method of Humanoid. Instead, you should search for the Humanoid’s Animator and call :LoadAnimation() on the Animator object.
Basically:
local humanoid = char:FindFirstChild("Humanoid")
local animator = humanoid:FindFirstChild("Animator")
local holdingAnim = animator:LoadAnimation(script.Animations.HoldingAnim)