I thought there was a feat for Investigator which allows then to as an Reaction use Devise a Stratagem for free starting around level 10. Did I remember the wrong eat or is it legacy content?
There's a level 2 feat to do it now, Person of Interest.
https://2e.aonprd.com/Feats.aspx?ID=5943
Do you mean this feat? Suspect of Opportunity is a level 10 feat that gives you a Reaction to use Person of Interest.