What is the function of the a key? My blender version is 2.91.
I pressed the a key to select all and cancel all selections.
At the moment I use the s key to select all the right side, and then the G key to move
In my user preferences I have enabled the "A" key to toggle select all or none. This is the old behaviour (pre 2.8)
However, the new default behaviour is to deselect with "Alt A"
"S" is typically the operator to scale the selection. ie - object, keyframes, handles or whatever the context is.
I wouldn't suggest changing that key ;)
You can use the use the square brackets [ ] to select all the previous and following keys
Or use the mouse with CTRL SHIFT and click with the mouse on either the left or right of the playhead.
I don't know if I have answered your question or not haha