I’ve tried a number of notes apps backed with “Sync with iCloud Drive” and often find it problematic. Usually the problems are on the Mac side, wherein my laptop does a bad job of pushing up small edits to existing files. I can force it with hacky things like viewing the folder in Finder, but that is a nuisance and easy to forget. The result is that I’ll open up Beorg/Obsidian/etc. on my iOS device and see a quite out-of-date version of the docs.
FWIW the non-drive iCloud Sync (core data?) works extremely well for things like Bear.
That's what I've heard. I passed on Obsidian for some other reasons, but during my eval I was pretty sure if I was to stick with it I'd pay for their sync service.
I think CloudKit is the name of the one that bear is using. It’s part of “iCloud”, but a different service (not the iCloud Drive). It seems to work well.
Obsidian has a few options, but can use iCloud Drive. As you note, it’s a bit hit or miss. Files take a while to sync. Sometimes the desktop won’t bother downloading a file. Hard linked files don’t seem to sync at all. (Obsidian’s paid sync service works well in my experience.)
FWIW the non-drive iCloud Sync (core data?) works extremely well for things like Bear.