How to set any song as ringtones

To make and/or use a song as a ringtone, you must first make that song suitable for a ringtone.

See the following Apple articles:

Create and manage ringtones -> Create and manage ringtones - Apple Community

Create a ringtone of your Logic Pro or GarageBand for Mac song

Create a ringtone of your Logic Pro or GarageBand for Mac song – Apple Support (UK)

Create Ringtones in Garageband -> Create Ringtones in Garageband - Apple Community

Then see -> Use tones and ringtones with your iPhone, iPad, or iPod touch

Use tones and ringtones with your iPhone or iPad - Apple Support