UISplitViewController.showDetailViewController() not working in iPhone version.

Since updating to Tahoe and Xcode 26 I have found that the UISplitViewController.showDetailViewController() is not working in the iPhone version of my app (it is a universal app). I'm just trying to show a detail view after a tap on a UITableView item. The iPad versions are all working correctly. Has anyone else experienced this or have any advice about what may have changed? Thanks in advance.

UISplitViewController.showDetailViewController() not working in iPhone version.
 
 
Q