Finding specific things
The file downloaded. The Downloads folder does not have it. Here is the order to check things in, and a trick most people do not know about.
Every browser keeps its own record, and it knows exactly where it put the file.
This is faster than searching and it works even when the file was saved somewhere unusual.
Open Finder, press ⌘F, set scope to This Mac, click + and choose Last opened date → within last → 1 day. Switch the window to list view and sort by Date Added.
Most "lost" downloads are found this way in about ten seconds, because you rarely remember the filename but always remember roughly when.
macOS tags downloaded files with a quarantine attribute that records the source URL. To read it:
xattr -p com.apple.metadata:kMDItemWhereFroms ~/Downloads/somefile.pdf | xxd -r -p | strings
That prints the page and file URL the download came from. Useful when you have a folder of PDFs and no memory of which site each came from.
~/Library/Containers and arenot saved to Downloads unless you save them.
~/Library/Messages/Attachments.Those three locations are all inside ~/Library, which is exactly where Spotlight will not look — which is why the file feels like it vanished.
Into a container folder under ~/Library/Containers/com.apple.mail. Opening one does not copy it to Downloads.
Yes, in each browser's settings. Safari: Settings → General → File download location.
Everywhere keeps track of every file on your Mac — including the folders Spotlight hides and drives you have unplugged. Free for a day, then $19 once.
Download for Mac