Is there a way to lock the value (y-axis) of an automation point, while moving it in time (x-axis)?
Yes, first press and hold the Shift key, then move the previously created handle. Restricts the direction in which no movement was made.
ah, nice, it works. thanks
To elaborate: It is called “constrained drag” and while Shift is the default, the modifier key can be configured in Ardour Preferences > Editor > Modifiers.