If you are a Mac user and searching for official Twitter app on Mac App Store, you would not be able to find it anymore. This loss is probably due to loss of third party support or perhaps relaunching it with enhanced features for Premium users and X branding.
Ever since Elon Musk launched Premium and Premium+ subscriptions on X, we observed that new features such as verified tick were no longer available on the Twitter client on Mac. For instance, tick mark for Premium users was not visible on the app. Also, any perk that you enjoyed on the mobile device or web browser version were not available on the app.
Infact, X stopped updating their Mac client all-together. They did not even bother to rename it to X, which further hinted they would be taking the app down in future, until it finally happened today.
Existing users can still download and install Twitter on their Mac. There is no word from X, previously known as Twitter when the app will come back on the official app store. May they will bring a brand new app under the X branding with features for Premium / Premium+.