Rogue Amoeba has updated Fission (https://rogueamoeba.com/fission/), its macOS audio editor. Version 2.4 brings revamped support for creating custom ringtones for use on the iPhone, iPad, and iPod touch.
iTunes 12.7 removed several features, including support for managing and syncing custom tones. This feature removal broke functionality in several current apps, including Apple’s own GarageBand app, as well as older versions of Fission. However, with Fission 2.4, users can once again save custom tones for use on iOS devices.
Fission runs on macOS and higher, with a free fully-functional trial available for download. While in trial mode, the quality of saved files is intentionally degraded via a series of fades in the audio. The unrestricted full version can be purchased for $29.