Are notes just for premium subscribers?

There are different ways to have dark mode using your browser settings. Example, if you're using chrome browser use the  shortcut:  ctrl+search+h or ctrl+shift+h to enter high contrast mode. There's also third party apps, extensions, themes, etc that can be added to darken the monitor. If you don't like those they make special gamers glasses that help. I've tried them they do help.

How often do they update dividend info?