How do I stop Apple Watch Series 6 alarms at 100% charge?

I have just exherited (ie from Daughter ) an apple watch 6. My Iphone is a 13.

The watch alarms at around 4am and the watch charging profile shows that this is when it reaches 100%.

The time screen and charging % screen alternate and a sound is generated. It stops when the watch is disconnected from the charger. No alarms are set on the phone and focus is not set up with any alarm times at all.

[Re-Titled by Moderator]

Original Title: Aple watch 6 alarms when charge reaches 100%.