Okay I mangaged to solve it.

Somehow I managed it to aktivate force dark mode only for http://localhost even though the feature "force dark mode" was turned off. Under opera://settings/content/forceDarkMode I was able to delete it again. Now everything is back to normal.

I'll leave the post here for others that might have the same problem

@hlehn You can right click > Disable Force Dark Pages to disable dark theme for that page and/or you can go to opera://settings/content/forceDarkMode

@nkgrzegorzewicz said in What happened to the Dark mode/Light mode switch in Easy Setup:

@leocg option "Force dark theme on pages" in Easy setup is already available in newest Stable version (115). You can find it when a theme with dark mode is selected.

Thanks.

@leocg Not until now. Thank you.

@leocg I just created an Opera account to thank you. Keep it up my man.