It’s currently available to the mobile app and mobile browers
Retweets will be more interesting in Twitterverse. Instead of just adding your own thoughts in a retweet, Twitter updated its mobile app, enabling users to retweet with photo, video, or GIF comments.
— Twitter (@Twitter) May 6, 2019
It may not be a big deal, but according to Twitter’s spokesperson, Twitter had to make tweaks to the layout by putting the original tweet in a smaller, indented box and making the photo/video/GIF comment in full.
The feature right now is available to Android and iOS versions of the app and to mobile browsers. Desktop users will need to wait a while before they can enjoy this feature.