Hi
@Irene2_ASUS,
Thank you very much for answering this: allowing location permissions to the weather app has done the trick.
Oddly, when rebooting the device during night time and dark theme (auto)enabled by sunset, it restarts again with the bright theme.
This doesn't happen when dark theme is switched on by a manually scheduled time: at night, it correctly reboots on dark theme.
Are you able to see this bug on your devices?