For that they use iframes, which have a different security system.

Because of the CORS settings on Google’s servers would tell your browser to not go forward with the request. There are two ways it could eventually be possible:

• By opening the video in a new page/tab that only contains the video, with the YouTube player, which defeats the purpose a bit.
• By installing an addon or an app on your device.

Fair enough, that’s interesting. I assume this only applies to the non-web clients. On the web, it would not be possible. You can verify by looking at the outgoing network requests on this random video for example: https://invidious.privacyredirect.com/watch?v=qKMcKQCQxxI

I’m pretty confident that you are wrong.

Invidious and YouTube piped (and LibreTube) by default load the videos server-side, as opposed to GrayJay, NewPipe or Smarttube.

It has advantages (mostly that your IP address is not shared with YouTube, and it allows users from countries where YouTube is blocked to still access it) and inconvenients (much harder to keep up when YouTube actively seeks to block them).

Smarttube next doesn’t require rooting the device, it can be sideloaded. Sideloading is not very complicated. Google is not trying to block any sideloading (at the moment, at least).

We don’t see many over here in Europe. I guess real Americans need to do real American work!

Joke aside, vans usually do the job better than trucks.

You can download videos and cut off sponsored moments in the video with sponsorblock.

GrayJay is pretty good!

LibreTube is also a good one. Basically an app for piped