Oh, it's really not anything impressive. I've just decided to treat %USERPROFILE% as for machine generated files only. I then have a new directory on C: where I put my documents/projects/etc (all in appropriate sub folders).
My config files are a bit more interesting, and are stored in a chezmoi[^1] repo. If I tinker with a program enough, I generally move its config into there so I can keep track of it and the changes (to make this easier I have a bat file in shell:sendto to add files/folders to chezmoi).
Thinking about this, I should probably move the chezmoi repo into my personal directory, and symlink it back to it's normal location.