From what I've learnt finally, there's no way to do it. But that's really unfortunate.
EDIT: Although not what I really hoped for, VLC media player actually allows you to view YouTube videos in their original resolution.
Open VLC
Go to Media (menu) → Open Network Stream... → paste the YouTube video URL in field under the label Please enter a network URL: and hit Play.
When the video has loaded, play the video, right-click on the video, under Video (menu item) → select Fullscreen option; then right-click again, and under the same menu item (i.e. Video) deselect Always Fit Window option.
The video should now be playing in its original resolution.
Google is releasing this feature slowly to individual channels currently. The larger more active channels will get it first. All Vevo and music based ones should be already offline, but they could miss a few non Vevo or Indie ones.
Best Answer
chrome://extensions/
and check for extensions that may be forcing dark mode preferenceCTRL
+SHIFT
+DELETE
and delete cookies which may store the dark mode preference because you are not loged in into YouTube