Is there a way to create and make custom ringtones that can be synced to my iPhone?

Hello--

I have a MacBook Air (OS Sequoia 15.4.1) and an iPhone 15 Plus running iOS 18.4.1.

On my previous computer and iPhone I was able to create custom ringtone with Ringer which automatically dropped the created file (under 30 sec.) into iTunes to synch with my phone. This all worked without a glitch. Now I have a new laptop and iPhone and cannot import Ringer-created ringtones to my iPhone. I have tried to import the file manually, but it never shows up on my phone nor is the "imported" file available to select from the Sounds and Haptics panel. Is there a way to create and make custom ringtones that can be synced to my phone?

[Re-Titled by Moderator]