Executive dysfunction and depression can present similarly but they are for inherently different reasons. Depression is mood-based while executive dysfunction is cognitive-based. Using your language, depression would include the "sads" while executive dysfunction doesn't. Hope this helps.

You could try contributing to an existing open-source project.

(a note-taking/thought-keeping app only for people who like to tinker and customize so wouldn’t necessarily recommend here)

It's as simple or complex as you make it to be. Obsidian can be used with core plugins only and work just fine.