Here’s what I do:
My Obsidian vault is just on my hard drive in my Documents folder.
On the same Mac, I have DevonThink index that Obsidian folder. This means that whatever I add to Obsidian is automatically also in DevonThink. This gives me the advantage of DevonThink’s superior search capabilities.
Note that IMHO what you don’t want to do is set up Obsidian in an iCloud folder and then also index that same folder in DevonThink. It’s too much syncing from different applications and at least in my experience, causes trouble.
Note that I do also sync my DevonThink database, using the CloudKit syncing that is built into DevonThink. The result is that I can view my Obsidian notes, via DevonThink To Go, on my iPad. It’s not full-fledged Obsidian because the links don’t work, but it’s enough for me to get basic access to my Obsidian notes when I’m not on my Mac.
Bottom line: either sync Obsidian via iCloud or Obsidian Sync, or do the DevonThink index, but DON’T TRY TO DO BOTH AT THE SAME TIME.
YMMV.
Lisa