Blockchain is a concrete noun, not an abstract noun — that may be why you can’t find anyone that can explain it top to bottom.

“Blockchain” as an abstract noun is a meme created by financial institutions and media but the reality is it doesn’t make sense to talk about it in an abstract sense; those that refer to it abstractly generally indicate a lack of understanding.

There are many different blockchains (the Bitcoin blockchain, the Ethereum blockchain, private blockchains, etc), would encourage you to speak with folks deeply ingrained in those communities if looking to better understand blockchains.