To fix, manually Link TVUIKit to the tvOS target. 1 - Select the Target in the Navigator 2 - Choose "Build Phases" 3 - In "Link Binary with Libraries" add TVUIKit.framework

You should add a "Foundation" tag to this Q.

Has anybody here seen this degrade again with Xcode 15? Xcode 14 was a pretty good year with this issue, felt like minimum issues. But with 15 it feels like it's been creeping back. If I'm in a loop of doing lots of dev and testing, sometimes I can only get a few Runs in before the Connecting between the two devices is lost. Incredibly frustrating.

That API is only available in visionOS today.

It all depends on the app, but in general you should be able to make the app work well on iPhone using the View Controllers and Storyboards you already have. You want to familiarize yourself with some older less fashionable concepts, namely Adaptivity. If you can find any old documentation on building a "Universal App" for iPhone and iPad, you'll want to read up on that as well. You'll also probably want to understand all the features of UISplitViwController.

Assuming you already looked, but just in case you didn't - is it not showing up in the Crashes Organizer?