Angela has a Mac running Big Sur and an iPhone. She used to be able to get Ring Tones using an app called Ring Toner. But it doesn't work anymore with Big Sur. Leo says you can make your own ring tones with Garage Band. There's no need to use a third-party app to do it. Garage Band is also available for the iPhone so that you can do it directly from your phone. Leo's TWiT show, Hands-on Mac Episode 19, will show you how to make a ring tone using the Apple Music app.
Third-party app options include Ringtones Maker.