I use obsidian with Synthing works like a charm sync it to my phone and laptop and to my server where it gets backed up

Obsidian works perfectly fine with iCloud Drive if you're bought into the Apple ecosystem. It also works well with Google Drive, but that doesn't play well with iOS.

Obsidian has their own sync platform independent of the rest. Diarly's $15/yr covers a handful of premium options, one of which is iCloud sync.

He's not using Obsidian. I use Obsidian with syncthing (not really an iOS option) so I pay nothing.