macOS Finder. It is hard to fathom how bad a file explorer could be if you have used only windows and linux file explorers. Finder is astonishingly bad. Default search is global, it means searching while you are in a folder will search across all documents. This can be changed, but search is even then far worse compared to windows or linux.

Sometimes Finder simply won't show certain files, and you need to do a mv from terminal to another folder, where you can see them in finder.