Just wanted to post this in-case anyone else was struggling. I spent a long time messing with splines and my blueprints but turns out they were not at fault.
If you are in selection mode, then editing splines work as expected.
However if you are in animation mode, you cannot right click a spline to get the context menu to add a new spline point, nor can you alt + drag off of a point to make a new point.
Weirdly though, while in animation mode you can create a new spline point if you select a point, start to drag on the translation gizmo, THEN press alt. This must be a bug.
Not being able to edit splines in animation mode is quite annoying considering I am animating with splines and control rigs (I created my own camera spline blueprint which works in sequencer as a spawnable binding, unlike UE’s cam rig rail). Switching modes back and forth constantly just to alter the spline path is a real pain.
Please bring the same spline editing abilities that exist in selection mode, to animation mode.