Update: this is fixed in 22.12.
I tried to enable an alert for 1 hour until sunset, but can't set the time till sunset and can't switch the alert on, it deactivates itself.
Settings -> System -> Time -> Alerts shows
If I select On, there is no option to set it to 1 hour, and it will stay On until I back out of the screen and it will be Off again (as above).
The alert Till Sunrise is on by default for 10 hours before sunrise. For that I can change the time, but can't switch it off.
I tried restarting the watch, and setting the alert with the Connect Mobile App (Android), which shows the exact same behavior.
If anyone has an idea how I can set the Till Sunset alert to 1 hour and the Till Sunrise alert Off, it would be greatly appreciated!