Lifeograph is a powerful note-taking application that can be used to keep an encrypted diary, to plan a journey, to manage todos and long term goals, to write down ideas in an organized way, to track regular activities and many more. Lifeograph strives to deliver an abundance of advanced features in a clean and streamlined user interface.
Main features of Lifeograph:
@XStein17 : you should have pushed the "edit" button on the top menu bar. Only after entering edit mode you can add new entries on whatever date you like. Linux Mint 20.2 Uma, Lifeograph 2.0.1 works fine here. But you really need to browse through its helpfile to learn how to do things (lots of things possible with this software).
Review is just of the flatpack version in the Mint repository as of 3/31/2020 - it is badly broken, can't add more days, only edit the entry it allows you to create when creating a new diary. I uninstalled it and reinstalled from the non-flatpack source and it works fine. Hopefully the flatpack version will be fixed someday. LifeOGraph itself seems to be a perfectly good journal program.