You can do it with iTunes. I just looked it up. I remembered it being easier than the instructions I found. Basically you are taking a 30 second clip of a song and renaming the file so it can be imported as a ringtone.

https://www.tomsguide.com/us/how-to-make-ringtones-iphone,review-6526.html

I used to make my own custom loops using audio software so I never went this route. It was just a matter of having the sound file in the correct format. But I admit that most people aren't going to go these steps to create a ringtone. It really should be as easy as selecting a song in your library.