Don't forget that Finder has customisable tags which sync perfectly across iCloud. They are a top-level browsing option on the iOS Files app. Probably you were thinking of something more tag-first but it does exist. :)

Personally I really like the file/folder model because I can sync the whole caboodle to my hard drive, copy it to a USB backup, possibly transfer it to another operating system, knowing that I've captured the whole story.

Are `invoice_2020_10_1.pdf` and `invoice_2020_11_1.pdf` children of their parent in the hierarchy, `invoice_2020_1`?

I handle this by making a google sheet for a project with links to the main files, many of which inevitably are cross-referenced to other projects or standards. It works well enough, and has a killer feature: if you move or rename a file, which I do all the time if documentation is refactored, the link doesn’t break!

It's really annoying how you can't easily make copies of directories anymore. They just create "Shortcuts" instead which act like symlinks. People though they were copies though and damn did we have a lot of accidentally deleted files these past few weeks. Also, their file recovery UX sucks.