Animating multiple objects in Blender is really unintuitive and difficult. It currently requires keyboard shortcuts and even then, keyframing properties that aren't in the ready-made Keying Sets is very confusing.

Key Selected Objects is an add-on that makes things a LOT more obvious and intuitive. Simply select the objects you want to animate, right-click the property, and choose 'Keyframe All Selected Objects.' Done!

You can also keyframe all multi-dimensional properties in a group (e.g. Location, Rotation, Scale, etc.) and delete keyframes! It also works with Materials that have matching Surface Shaders (e.g. Materials with Principled BSDF).

Included in the Ultimate Animators Bundle!