I want this event / observer (..)
But only triggered if the track was selected my using left mouse click.
It doesn't exist, nor is it likely to.
We do not provide such low level methods to hook into Renoise's main GUI events. It's only possible to do such things with your own custom tool GUI built using the ViewBuilder widgets.
What exactly do you intend to do when the track has been clicked? Perhaps there's an alternate method or workaround.
Btw. what is the difference here^ to:
renoise.song().selected_track returns a renoise.Track object, which refers to the actual track itself as it exists in the entire song, with its DSP chain, mixer properties, number of visible note columns, and so on.
renoise.song().selected_pattern_track returns a renoise.PatternTrack object, which refers to the pattern data from a single track at a given point in time within the sequencer, with each pattern line, note column data, effect column data, etc.