The app downloads assets consisting of custom fonts using tags from On-Demand Resources, registers them in the system font, and provides them to other apps such as Freeform through UIFontPickerViewController.
Custom Fonts that were applied well until iOS 16 appear as Helvetica starting from iOS 17 and cannot be used. As the font list appears in the device's Settings > General > Font, the font downloaded from On-Demand Resources is registered in the system font. It has been confirmed to occur particularly frequently starting from iPhone 15 and iOS 17 and above.
The app requests download from On-Demand Resources with NSBundleResourceRequest along with tags, receives assets in response with conditionally beginAccessingResources and beginAccessingResources, and then registers them in the system using CTFontManagerRegisterFontURLs.
