If you have or have created the “official” Obsidian folder (with the icon) in iCloud Drive and your vault is in there but are still having issues, you could try:
- iOS Settings > Apple Account > iCloud > Saved to iCloud > Drive > Apps syncing to iCloud Drive > toggle Obsidian off-on and reboot the phone.
- iOS Settings > Apple Account > iCloud > Saved to iCloud > Drive > toggle Sync this iPhone off-on and reboot the phone.
These steps have helped some folks.