> I use dir trees for code ofc, but everything else is flat in my ~/Documents.

Which is great, but on all major OSes you'd eventually hit performance issues with flat directories like this. Might not be an issue in month one, or even year one, but after 10 years of note taking/journaling that approach will show the issue with large flat directories.

So eventually you'd need to shard it somehow, so might as well start categorizing/sorting things from the get go, at least in some broad major categories at least, because doing so once you already have 10K entries in a directory, it sucks big time to do it.