Did some testing today. Seems this is not specific to NBC App, but other Android Apps as well. What people have noticed is videos will start dim, then only return to full brightness after the SeekBar is touched. The SeekBar is the progress scrub bar at the bottom of the video.
Seems launching the NBC App via ADB brings up video puts video into a dimmed state as if the SeekBar was active. You can manually clear this by opening the live guide for a moment, then exiting. This brings the video back to normal brightness.
From this Reddit Thread, you can see it is not just NBC Apps, but by comments, many Android apps:
https://www.reddit.com/r/revancedapp/comments/1bb44sw/youtube_screen_becomes_dim_and_on_screen_buttons/
Since the NBC App does not have any Accessibility Options, I assume the next best step would be to (possibly) modify the Activity to set a SeekBar brightness to max. The link below has some ideas, but I'm not a programmer, so I will leave to you more experienced types.