After trying a few note-taking apps, I ended up using Apple Notes. It was super fast on macOS and iOS. This was more or less my thinking: The syncing was good and it worked offline. But it had a couple of drawbacks. The format is not open. There are some scripts to reverse-engineer the Apple Notes SQLite database1, but that still needs a computer with iCloud sync, otherwise you can’t get the Notes.app SQLite database on your disk.
