Currently most popular browsers and apps implemented "Dark mode" seamlessly without the need to restart the browser when the operating system switched the app theme to dark. With Opera as an exceptional case which I need to restart the Opera every day when my Windows app theme switched to dark mode because of sunset. To me, I think there should be an option to automatically switch like what other apps or browsers did. I knew some may not like the switch of theme automatically, that's why I suggest at least "light", "dark", "system default" these three options for color choosing. Here attached the current situation from other browsers developer version or similar version:
No option to choose, follow system by default, can install more themes
Firefox Alpenglow is a theme that change dynamically based on system color
Dark themes only
Can change theme with scheduled time and let user to choose which theme for both light theme and dark theme. I think it is the best option but it doesn't change their start page wallpaper with theme which the developers said they are working on that.
Hopefully, I can no longer manually restart Opera in the near future.