2 problems
1 - there is no open link in new tab option, only new private tB or wondow
2 - light mde is set but all tabs have dark background. Your docs say:
" New tabs page’s settings menu should adjust itself based on the user’s currently set theme, whether it be Light , Dark or the theme set on the OS level.’
Perhaps you should be ,ess aggressive about pushing features and updates and focus on getting things right