The journal
Today has a page.
Days with an entry get a mark. Tap one to read it back.
Entries are never edited here: the page you wrote stays as you wrote it, and notes carry their own date.
The export is one plain file holding the journal and the check-in. Save it to iCloud Drive and it is backed up from then on, and it will still be there for a new phone. Importing merges rather than replaces: an older file cannot wipe a fuller journal.
We do not receive any of this, store it, or have any way to read it. Because we keep no copy, there is no copy: the export is the backup, and the privacy page walks through it.