As I look through Flathub, maybe KOrganizer is the closest thing to what I'm looking for, although it's got KDE's disease of being hideously overcrowded with every possible feature.

I think what I'm after is somewhere between KOrganizer and RedNotebook. I currently use RedNotebook to keep my journal, which in my case takes the form of talking about my day, what I did, what I'm thinking, and sometimes what I'm planning. It has no todo list functionality, but I can use it as a sort of note to self thing, it has a search function that allows me to easily look back. I almost always have it open and running on my computer.

imagine RedNotebook, but with some todo and checklist functionality so that I get today's page, there's a blank page for a journal entry so I can record what I did today, and maybe a separate side pane for daily tasks, maybe several panes stacked vertically for "regularly scheduled" where daily stuff like "change cat's water dish" or weekly stuff like "garbage day" or monthly stuff like "water bill due" could pop up, and it would serve not only as a reminder to do those things, but a record of having done them. And maybe another pane for ongoing stuff, like...say I want to list all the things I want to build in the wood shop this summer; this might not be time based but just a running checklist. It would be kind of cool to be able to look back at that and see when things were added, checked off, or removed.

Lifeograph might be designed for this but 1. damn if I can figure out how it works and 2. it won't stop shining bright white rectangles at me.