In Animate software, the two key frames of shape tween animation are shapes and cannot be grouped. Then right-click the middle frame and select "Create tween shape animation".

For mask animation, you can select a layer and then right-click to select a mask layer, or you can choose the option of adding a mask layer.

You can refer to the tutorial of Flash software.

How to Animation Digital Switching Animation and Mask Animation

How animation realizes digital switching effect through shape adjustment