Back in the 90ies my uncle always got a book for the car hee owned which would explain how to disassemble it.
But me and my dad never bothered with the book, just got to work on it and figured it out on the go. The biggest thing I replaced in my car was the whole Chassis.
But yeah in the new cars there is less mechanical stuff and more electronics so it’s getting difficult.
The only place I can think off was YouTube, or if you can find a book like my uncle always had: https://onlymanuals.com/volkswagen/passat/volkswagen_passat_b3_workshop_manual_passat_b3
I was very surprised about the Synology video too. There was no critical word about anything in it.
Sure they offer a selfhosted sollution for things but their software is closed source for example.