I can get a launch image to work, but not any of the other properties like background color. And the image doesn't fill the safe areas so it looks bad.

I'm running Xcode 15 and SwiftUI, and @biztos answer is what did the trick for me. All the tutorials I found talked about an info.plist file which doesn't exist anymore (at least not explicitly), and to add the full relative font path including the directory name the fonts are in. The full gambit is to select your project in the project explorer (the left side panel that shows your files). Navigate to the Info tab, under the Custom iOS Target Properties section add a new string array key/value pair with the key name being "Fonts provided by application". Add each font file name without any paths associated with it. An additional step I found somewhere was to also add "Fonts" under the Signing & Capabilities section. I'm not sure if this was required or not bc I tried a lot of stuff before I got it working. Side note: It wasn't clear for me how to add a new key to the info section. Just click the plus icon on any of the rows and it'll let you add a key. Not very clear UX but oh well.