Technical library: Academic Topic/subtopic/ then pdf title
Music: I use beets now, which imports and organizes everything
Household: Accounts folder, Mortgage folder, Appliances folder with subfolders for each appliance containing manuals, photos, and maintenance info.
Systems folder: subfolders for various IT systems and lots of related data in them
Projects folder: topic/project name mostly, sometimes with subtopics
Documents: YYYY/topic for things that I can find by year later, like taxes, licenses. Also used as longterm archive for projects.
Software/repo for various repos that don't fit in other categories (not too happy with this)
/opt/venvs for lots of python virtual environments.
Pretty much everything is in a mirrored ZFS pool with auto-snapshots (for rewinding in the event of accidental deletions) and occasionally dumped to external drives put in fireproof/floodproof safe (and taken offsite).