With Input Manager becoming deprecated after Unity 6.3, your scripts using Input.GetKey, Input.mousePosition, or GetMouseButtonDown will need to change. Modern Input System covers all these, and is just as simple for basic needs! Check out my cheat sheet to see how easy it is to convert your code to stay up to date. BUT for OnMouseEnter or similar MonoBehaviour callbacks they do NOT work with the Input System! You'll need to switch to event interfaces like IPointerEnterHandler, plus make sure you've got a Physics Raycaster & EventSystem in your scene. So upgrading that part is a bit trickier, but the rest are easy.