The other method that I am familiar with is by using another computer and iTunes/Music app. However, I'm not sure if you'll find the process more user-friendly than Garageband (I personally found it somewhat convoluted). Essentially, you have to convert an audio file (mp3 extension) that is less than 30 seconds to one that is encoded with Apple's AAC encoding (m4a), and then convert it to a ringtone file (m4r).
When I did it I followed the steps explained in the first half of the following article: https://www.macworld.com/article/616018/how-to-custom-ringtone-iphone.html