The download goes to your Downloads folder. Click the downloads arrow in your browser toolbar, or open Finder and pick Downloads from the sidebar. Press Command and J in Chrome for the full list.
Because the file is written straight to storage rather than into an app’s private sandbox, anything on macOS Ventura, Sonoma and Sequoia that can open MP3 can reach it. There is no library to import into and no proprietary folder to dig through.
MP3 opens in QuickTime, IINA, VLC, iMovie and Final Cut Pro, and more broadly on every music player ever made, including car stereos, old iPods and cheap MP3 players.
This is the practical reason MP3 is offered at all. MP3 is a genuine conversion, not a rename. The source on X is AAC, so 192 kbps is chosen deliberately: it is comfortably above the point where the conversion would become the limiting factor rather than the source. If a file has to work on a device you do not control, or software old enough that nobody updates it any more, MP3 is the option least likely to be refused.
You are downloading MP3 at a constant 192 kbps. The sound track on its own, converted to MP3 at 192 kbps.
It is worth being precise about what that means for quality. X re-encodes everything uploaded to it, so the source already sits one generation below whatever was originally recorded. Nothing here can recover that. What is within our control is not adding a second generation, and the video path avoids it entirely by copying rather than converting.
If Safari opens the video in a tab instead of saving it, hold Option while clicking download. Safari previews media it recognises, and Option forces it to write the file to disk instead.
If the post will not load at all, the account is the usual explanation rather than the device. Protected accounts, deleted posts and region-restricted posts cannot be read, because the media is not publicly available to fetch. Copy the link from the post’s own page rather than from a quote, a notification or a search result, and most remaining failures clear up.
Copying links gets tedious after the third or fourth video. There is a shortcut: in the address bar of any X post, replace x.com with downloadthisx.com and press enter. The download page opens with that post already read, so there is no copying and no pasting.
On Mac this works in Safari, Chrome, Firefox or Arc exactly as it does anywhere else. It is the same page you are on now, reached by a different route.
Only public posts can be read. Protected accounts, direct messages and anything sitting behind a login are out of reach by design, not by oversight.
Saving a clip for yourself is ordinary. Republishing someone else’s work as your own is not, and downloading it does not change who owns it. The author keeps the copyright whatever folder the file ends up in on your Mac.