I’ve been away from Ardour for a while, but last I used it, it had an Edit playhead, a blue one, as opposed to the red Play playhead. has that been removed?
Yep you have been away a while…
That hasn’t existed since pre-2.0 IIRC.
The nearest equivalent is to set the edit point to “Marker” and then create/select a marker. It will draw a similar blue line through the tracks, and can be dragged around at will.