X (formerly Twitter) can no longer be accessed in the Mac App Store, suggesting that it has been officially delisted. Searches for both “Twitter” and “X” Twitter can no longer be accessed in Apple's Mac App Store, suggesting it has been officially delisted.
This article says the app was removed because it still had the Twitter branding and they have a new app instead, and the old app was ad-free. Why not just use the regular web browser?
I used this years ago when I was still on Twitter, it was a good app. It actually used windows properly instead of stuffing everything into a single window (for example making a new tweet opened a separate dialog) and everything. Rare to see nowadays