This might be exactly what I need.
Currently, I use [Obsidian](https://obsidian.md/) to keep notes and [Syncthing](https://syncthing.net/) to sync them between devices. A major downside of this is that the devices have to be online at the same time for them to sync.
Thank you! Duck doesn't require devices to be online at the same time, the sync works asynchronously in each device. So I'm happy if it meets your need!