As the forum denies to create a new topic for my question:

Why are GOG's videos (from YouTube) worse than watching them directly on YouTube?

Take the game Deliver At All Costs as an example. The first video, right from the opening seconds:

https://www.gog.com/en/game/deliver_at_all_costs

https://www.youtube.com/watch?v=e9WOW07suws

The three screenshots:
https://postimg.cc/gallery/68dFgwL

I set the videos explicitly to 1080p60. Compare the screenshots I uploaded. The GOG version is clearly blurry throughout the entire video! On the other hand, the YouTube version is visibly better.

The third screenshot is from S team, which doesn't reveal the video specs, but I assume it's 1080p since it looks very similar to the YouTube screenshot. All three screenshots were taken on the same computer (Windows 10, latest Brave browser), using the same internet connection, full screen, untouched PNG zero compression. I ran the three tests a few minutes apart from each other. I also made sure to let each video play for about 30 seconds before taking the screenshot, to ensure the video had time to buffer and reach quality. So why are there such differences?

In general, I find that S team videos look better than GOG. Please be tolerant, it might just be my personal bias for preferring to check game details there rather than here.

But regardless of any specific issues on GOG's side, the videos don't look exactly the same in visual quality, even though they're arguably from the same source. There must be a number of factors I'm not aware of. Does anyone have knowledge to share, like web browser settings, tweaks, or anything else, to help get the best video quality possible anywhere?