I am very new here and so take all with a grain of salt. but I have read some pile of text today and here are some start-links that gave me some impression.
Customize eDrive synchronization settings speaks of Application settings toggle will affect synchronization for device settings. Maybe you can see which apps get synced and your question is about THOSE apps only?
[HOWTO] Sync your contacts, calendar events, email, notes and tasks speaks about diverse apps that are being synced after activating that. Maybe you can find each “messenger message” app somewhere there? Mail seems to be treated separatedly.'form messenges (where is all this TelegramSignalWattsappThreema vs SMS already is a rabbit hole on its own)
For everybody reading my post: I also would be very thankful for a deep dive into the internals and in depth documentation of the syncing and magic integration. I would prefer to KNOW what is under the hood before I open my private date to someone else’s “cloud” computer.
Bear with me: new here! 