Sync should be boring before it gets clever.
Especially for notes. Markdown files are easy to understand until the sync layer turns them into a magic trick. I want to know which folder is canonical, what moves where, how conflicts are handled, and how to recover when one machine goes stale.
That sounds like plumbing because it is plumbing.
The temptation is to design the future architecture first. The better note says what is actually running. What sync path exists. What is backed up. What happens when it fails.