Just to clarify the license:

- The desktop, mobile, cli apps and clipper are open source. They can all sync for free with any of the supported services - Dropbox, OneDrive, S3, Nextcloud, WevDAV and the file system (some people use SyncThing). All this will always be free and open source.

- Joplin Server is free for personal use, so you can self host it. It was MIT originally, but I had to change to a more restrictive license because companies were selling access to it and I don't think it was fair that I do the work for free, and all they have to do is run `docker-compose start` and sit there and make a profit. But if it's for yourself, family or friends then it's free and will remain so.

They are just selling their own sync option. Since Obsidian store all the notes as plain markdown files on disk you can just use another sync option like Dropbox or even git.

Or SyncThing (but download SyncTrayzor to make using SyncThing easy)

I’m looking for a note taking app that does iOS<—>Linux syncing. Joplin seems to be able to do it via Dropbox.

No. Joplin can sync using different ways and backend (webdav etc). It has also crypto and wysiwyg editor AND versioning. It's the definitive personal wiki on all platform. It has also a terminal gui LOL

not as far as I know. I've been using it for over a year and think that there's a free way to do everything on your own, and the devs and mods even help out on Discord for people to set it up. You can pay for the Sync or hosting service, but everything is optional since there are plenty of other options.