I make my own ringtones out of music I like. For example, I just made one out of Intermezzo for String Quartet, WAB 113, by the Vladimir Mendelssohn & Sonar Quartet. Why, you might ask? If you play this (it's in the Apple Music store amongst other places), and you are a 1940s detective movie buff, you will note it's the awesome theme played at the beginning of the Sherlock Holmes movies with Basil Rathbone!
Anyway - I digress. Here is how I simply create my own ringtone. (Note - in my case, I have a subscription to Apple Music, so I have to PURCHASE the song and DOWNLOAD it to make a ringtone from it. So yes I am paying 99 cents for a song - it's not a 'free' ringtone, but I thought I would add this technique here because it seems like a small price if you really want to use quality music for your ringtones.)
I do all this work in Apple Music app on my MacBook Pro.
1. Select a song to use as the source. You cannot use an Apple Music item, or anything that is in the cloud. It must be owned and downloaded.
2. On the Get Info > Options tab set start and stop times no more than 40 seconds apart, or 30 seconds for text tones.
3. Under Apple Music/Preferences/Files, click on Import Settings.
4. Under Import Using, Choose AAC Encoder. Under Setting, choose High Quality 128k.
5. Use File > Convert > Create AAC version.
6. Reset the start and stop times on the original track so you will hear the whole song the next time you play it.
7. Right-click on the new shorter copy of the song and click Show in Finder. From Finder, move the song to the Desktop, for copying to iPhone/iPad.
8. Delete the new entry from the music library, you don't need it there any more.
9. Change the file extension from .m4a to .m4r.
10. Use the app iMazing (free! In the Apple Mac store); connect iPhone or iPad to laptop via cable.
11. Drag and drop the .m4r ringtone file into the Ringtone section for the connected iPhone/iPad.
The song is now available on your iDevice and will show up in Settings/ Sounds/ Ringtone, to choose and use.