Cross system / OS landscapes can make it nearly impossible without Obsidian Sync. It's okay for Android & Windows, but if you throw an iPad into the mix, you can't really find a local/cloud sync for them all. iOS especially has some limitations on how apps can access files, so your only options are iCloud or Obsidian Sync.
For more info see here: https://help.obsidian.md/Getting+started/Sync+your+notes+acr...