I have found a possible cause and a workaround to fix this problem. I found out that my pencilInteractionDidTap is not called if the view-controller that contains this interaction is presented via my own custom modalPresentationStyle. (Using my own Transitioning Controller) If I change the modalPresentationStyle to a standard (.fullscreen) when presenting the above controller, the interaction works fine. The problem could either be in my own transitioning code, or iOS. I have not investigated that part. Also, when I was experimenting by creating a fresh app from templates, I found out that I had to pair my Apple Pencil at-least once even if it was already paired. Not sure if the pencil needs to do re-initialization in order to send the interactions to the new app.

I have the same issue. It is my understanding that the old 'detail' paradigm no longer applies with the new two-column / three-column styles. It means, that there is no master/detail now, but just primary, supplementary, secondary and compact columns. So even if showDetail works in some cases, it is actually an anomaly. Until we get a first-class segue for 'columns' (eg. showSupplementary, showSecondary, showCompact), we may have to just set things programatically using setViewController(_:for:) methods. Furthermore, I don't think the new documentation prescribes any specific direction in which the settings should be made (eg. Primary -> Supplementary -> Secondary). For example, an app may choose to populate supplementary and secondary at the same time (eg. Supplementary showing the overview of Secondary content), or secondary may drive the supplementary column. (eg. supplementary shows a snippet of secondary content). For these reasons, defining new segues may be difficult, and so we may have to rely on settings things programatically.