Otherwise the free Obsidian has everything, and there are other plugins for self hosted syncing that don't use the paid service.
For those that want to sync without paying, many use syncthing, though I don't think this is a feasible workaround for iOS users.
There are some other syncing methods that I haven't really looked into.
If don't know how or can't be bothered, you can pay for Obsidian Sync - which Just Works.
I tried to roll my own syncing with syncthing and iCloud and Dropbox. In the end I spent so much time debugging and dealing with files clobbering each other mid-sync I figured out $4/month to support a project I use daily isn't too much.
Zero problems since and I use Obsidian regularly on 4 different devices.
I use DriveSync on Android to sync selected Gdrive folder to my phone.
It works.