Since roughly 1 year ago I have been making "leftoff" comments in my code, whenever a work day ended or so, with a few notes on what I was doing and what I was about to work on next.

And I recommend it, I think that's good practice. Because I forgot to do it on friday and I have no GOD DAMN CLUE what I was working on :|

I just use a notepad on my desk
#oldschool

I have a whole folder next to my projects in version control with a bunch of markdown files that document processes and structures. I use VSCode so I also often embed logical structures in yml and interface definitions in typescript code blocks so that they get syntax highlighted. When I publish something I merge these notes into the source tree, turning design notes into concise comments, usage notes into a README and putting what's left (mainly hopes and dreams) into a private Obsidian notebook.

I use a "pagefile.md" in that folder to dump my thoughts before concluding work, but that's almost never committed.