Every time I use Bezier interpolation on Animation Curves keyframes, I have to relearn how they work and how to control and manipulate them.
You have to select a keyframe control point first and then press the icon for Bezier curve interpolation.
If a keyframe control point tuns grey when you click it, that means it has a Bezier handle available that can be dragged out and used.
Sometimes, two Bezier handles are available as indicated by clicking the keyframe control point when a Bezier handle is already out and the control point turns grey again.
If a keyframe has only one Bezier handle, it gets another one if you enable an adjacent keyframe for Bezier curve interpolation.
If you do Shift+click then you can select more than one keyframe before you press the icon to enable Bezier curve interpolation. The number of Bezier control handles you get in that situation seems to depend on whether or not there is another keyframe control point adjacent to the keyframe on both sides of it or if it is at the end of a sequence.
It’s confusing but it does work.