This method worked to add custom ringtones/notification sounds to the GW5 (as well as GW4) prior to the recent GW5 update AVK7:
forum.xda-developers.com
Stated in post #7, which is summed up here:
(1) use the wearables app to transfer the ringtone/notification in MP3 format to the watch.
(2) Then a file explorer to copy the ringtone to internal memory/ringtone and/or the notification to internal memory/notification
(3) Press and hold home button and select power off
(4) Press and hold home button to turn watch back on
(5) wait (even for a little after the watch has finished booting)
They then show up as a ringtone/notification but ONLY on the watch; you can't make the change on the phone as it doesn't see them in the wearables app.
Since the update any added mp3 files no longer show up in Settings>Sounds and Vibration>Ringtone list on the GW5. Any ideas as to why the update changed this behavior and what is a workaround?

Add custom or replace default ringtones or notification tones. Is it possibile?
Hi guys, Is there a chance to add custom ringtones or notification tones to watch 4? Or maybe to replace the default one with other files with the same name.... It's not working to add files trough Manage Content/Add Tracks

Stated in post #7, which is summed up here:
(1) use the wearables app to transfer the ringtone/notification in MP3 format to the watch.
(2) Then a file explorer to copy the ringtone to internal memory/ringtone and/or the notification to internal memory/notification
(3) Press and hold home button and select power off
(4) Press and hold home button to turn watch back on
(5) wait (even for a little after the watch has finished booting)
They then show up as a ringtone/notification but ONLY on the watch; you can't make the change on the phone as it doesn't see them in the wearables app.
Since the update any added mp3 files no longer show up in Settings>Sounds and Vibration>Ringtone list on the GW5. Any ideas as to why the update changed this behavior and what is a workaround?