That's like pointing to https://www.kingjamesbibleonline.org/ and claiming this is one true Christianity. There are some 45 000 distinct Christian denominations on the planet, each with different beliefs and practices, doing exactly that, and each claiming they're the ones getting it right.
Except that in reality, a subset of the Bible that all those denominations agree is the literal, true, OG Word of God, is... what I linked above, +/- a book or three. The source material is not the problem here - only that everyone has their interpretation.
Similarly, everyone agrees that the Agile Manifesto is the OG source of Agile faith - and then everyone claims their own particular interpretation of it is the True Meaning anyway.
The Agile Manifesto is what kicked it all off. Scrum, etc. and all the other "agile" stuff that people complain about now just latched onto the word. The equivalent would be that if Jesus had personally written down his thoughts and we still had a copy floating around, you totally could point to that and say that it's the true, original version and anything else is just an interpretation that should be taken with a grain of salt.