https://superhivemarket.com/products/key-selected-objects

• Animating multiple objects in Blender is really a non-intuitive and complex process. Currently, this requires keyboard shortcuts, and even in this case, creating keyframes for properties that are not in the ready-made sets of keyframes is very confusing.
• The Key Selected Objects add-on greatly simplifies and makes this process more understandable. Just select the objects you want to animate, right-click on their property and select "Create keyframes for all selected objects". Done!