Which sources? How do I know I can trust the sources that I found?

They can, but they usually don't, unless forced to.

(Incidentally, not that different from LLMs, once again.)

How do you even know what original sources to read?

There's something called bibliography at the end of every serious books.

I am recalling CGP Grey's descent into madness due to actually following such trails through historical archives: https://www.youtube.com/watch?v=qEV9qoup2mQ

Kurzgesagt had something along the same lines: https://www.youtube.com/watch?v=bgo7rm5Maqg

And yet here you are making an unsourced claim. Should I trust your assertion of “most”?