Given that I'm an Android developer and know how to use Android, I'm yet again amazed by Google's ability to disguise options and to change them with every release (in addition to the device manufacturers doing the same thing).
What I want to achieve: disable auto-sync of all data with Google (including app data, contacts, SMS, calendar, ...)
The way it doesn't work on my device is by following the instructions you get from googling "android how to disable Google sync". I'm not stupid ;) I do know how to google.
I have a Sony Xperia XZ1 Compact with Android 8.0 Oreo. I'm unable to disable synchronization. Here are the screenshots:
Note: On the last screenshot, when scrolling down the list, I can see "Google Play Movies & TV" where it explicitly says "Sync is OFF". It doesn't say that for the other items.