The solution you seek will involve different approaches, some appropriate to the 3D portion(s) of the scene, some suited to the UI.
For the 3D camera your choices are to adjust the camera’s view position, or else adjust its field of view.
Since Camera stuff is pretty tricky, you may wish to consider using Cinemachine from the Unity Package Manager.
For the UI stuff it is much more involved. Here are some notes:
Here are some notes on UI Anchoring, Scaling, CanvasScaler, etc: