Keep a journal.
I have a single journal for daily events, in excel of all things.
I have a title column, date, related to (Linux, Tailscale, Health, etc) then a Notes column. This way I can filter on the related to column and search it.
I have links to OneNote pages (or just titles), and could easily do the same with Obsidian or anything else. There are years of notes in it now. Anything I've fixed is in there, so easy to find again with my own wording (which is how it started, then I realized keeping a separate personal journal made it harder to see things in general, or connections specifically) .
On my phone I use an app called... Memento. It's like excel, but designed for a simpler UI. Easy for me to create new databases on a whim, or simply add info to one.
I believe many people witg ADHD have a working memory deficit too, so getting new info into long term memory is more crucial for them.
I also agree that handwritten is generally best for journals/notes like this, I just needed it to be searchable.