First, go to https://www.wowhead.com/sounds/ and download the sound in question. There is a rather nice search function to narrow things down.
Next, go to one of the many online converter sites and convert the file to the M4R format. Some of them have a daily limit but there are many that seem to work. I used this one. https://www.online-convert.com/
Next, open the GarageBand and import the file.
Here are the instructions from Apple Insider in case they go missing from this site. https://appleinsider.com/inside/ios-17/tips/how-to-create-custom-ringtones-in-ios-17
Assign a suitable name to the project and save it in iCloud Drive by hitting "Save."
On the iPhone, launch GarageBand. Press the downward-pointing arrow at the top left, followed by "My Songs."
Click "Browse" and locate the stored project in iCloud Drive. Press and hold the project, then choose "Share."
In the "Share Song" menu, opt for "Ringtone." Enter the ringtone's name and hit "Export."
Navigate to "Settings" and go to "Sound & Haptics." Then, press "Ringtone" and pick the newly created custom ringtone.
Now every time I get a calendar appointment reminder, my Hyena lets me know.