There is a similar thread from someone experiencing the same issue as yours:
One thing to add here would be to check if you are even using the old input system, which you can double check in the Player Settings --> Player expand the Other Settings drop-down menu and look for Active Input Handling, but if you can use the Input.GetKey() methods than you probably are already
Also make sure that you have configured the Key or Mouse Button as the type in the Input Manager
Let me know how that goes